Blueberry Buttermilk Snacking Cake (8×8) with a Tender Crumb

Blueberry cake should be simple to make, easy to slice, and good both warm and at room temp. This version hits those marks. It starts with cake flour for a fine, soft crumb, leans on real buttermilk for gentle tang and a steady lift, and finishes with a cinnamon crumb that bakes up crisp and fragrant. The result is a square snacking cake that stays moist for days and cuts cleanly into tidy pieces you can pack, share, or leave on the counter for passing forks.

The payoff is in the texture. Cake flour keeps the crumb delicate. Buttermilk reacts with a little baking soda to help the cake rise evenly. Blueberries stay juicy without turning the whole interior purple. The crumb topping adds sweetness and crunch so you get contrast in every bite. Nothing fussy, just a reliable, Oregon-kitchen kind of bake you can make on a weeknight or for a relaxed weekend breakfast.

If you like a slightly lemony note with blueberries, there is an optional zest in the batter. It brightens the flavor without crowding out the buttermilk.

What Makes This Cake Work

A small square pan means fast baking and easy storage. Cake flour lowers the protein content compared to all-purpose, which gives a finer, softer structure. Buttermilk’s acidity tenderizes the crumb and supports leavening. A mix of baking powder and a small pinch of baking soda gives a steady rise with no metallic taste. The crumb topping brings sweetness and texture so the interior can stay soft and not overly sweet. That balance is the point: a cake you want to slice again after it cools.

Recipe: Blueberry Buttermilk Snacking Cake (8×8)

Yield, Time, and Equipment

• Servings: 12 small squares or 9 larger pieces
• Active time: about 20 minutes
• Bake time: 38 to 45 minutes
• Total time: about 1 hour, plus cooling

Required equipment

• 8 inch by 8 inch metal baking pan
• Parchment paper
• Two medium bowls and one large bowl
• Hand mixer or stand mixer (paddle) or a sturdy whisk
• Digital scale (recommended) and measuring cups/spoons
• Microplane or fine grater if using lemon zest
• Cooling rack
• Toothpick or thin skewer for doneness testing

Ingredients

For the crumb topping

• 3/4 cup (90 g) cake flour
• 1/4 cup (50 g) granulated sugar
• 1/4 cup (50 g) lightly packed brown sugar
• 1 teaspoon ground cinnamon
• 1/8 teaspoon fine sea salt
• 6 tablespoons (85 g) cold unsalted butter, cut into small cubes

For the cake

• 1 1/2 cups (180 g) cake flour
• 3/4 cup (150 g) granulated sugar
• 1 1/2 teaspoons baking powder
• 1/4 teaspoon baking soda
• 1/2 teaspoon fine sea salt
• 6 tablespoons (85 g) unsalted butter, softened but still cool to the touch
• 1 large egg, room temperature
• 1 1/2 teaspoons vanilla extract
• 3/4 cup (180 ml) cultured buttermilk, room temperature
• 1 to 1 1/2 teaspoons finely grated lemon zest, optional
• 1 1/2 cups (about 225 g) fresh blueberries, patted dry
• 1 teaspoon cake flour for tossing the berries

Preparation Instructions

1) Preheat and prepare the pan

Heat the oven to 350°F (175°C) with a rack in the center. Line an 8×8 metal pan with a strip of parchment that runs up two sides to form a sling. Lightly butter or spray the pan and the parchment.

Why it matters: Metal pans conduct heat more predictably than glass in this size, which helps the center bake through without over-browning the edges.

2) Make the crumb topping

In a medium bowl, whisk the cake flour, granulated sugar, brown sugar, cinnamon, and salt. Add the cold butter cubes. Work the butter into the dry mix with your fingertips or a pastry cutter until it forms pea-sized clumps with some sandy bits. Squeeze a handful; it should clump and hold. Chill the bowl in the fridge while you mix the batter.

Goal: A cool, clumpy streusel bakes into defined crumbs instead of melting flat.

3) Mix the dry ingredients for the cake

In a large bowl, whisk the cake flour, sugar, baking powder, baking soda, and salt until uniform. This prevents pockets of leavening.

4) Cream butter and add wet ingredients

In a separate bowl, beat the softened butter until creamy, about 30 seconds. Add the egg and vanilla and beat until smooth. Add the lemon zest if using. Pour in about half of the buttermilk and mix just to combine. The mixture may look a bit curdled. That is normal.

Note on temperature: Room temperature buttermilk and egg help the batter come together quickly without overmixing.

5) Combine wet and dry

Add the butter mixture to the bowl of dry ingredients. Add the remaining buttermilk. Mix with a spatula or on low speed just until the batter is mostly smooth and no dry flour shows. Scrape the bowl. Do not overmix. The batter should be thick but spreadable.

6) Fold in the blueberries

Toss the blueberries with 1 teaspoon cake flour to help them stay suspended. Gently fold the berries into the batter. A few burst berries are fine. Avoid streaking the batter purple.

7) Fill the pan and top with crumbs

Scrape the batter into the prepared pan and smooth the top. Scatter the chilled crumb topping evenly over the surface. Do not press hard. A light pat helps the crumbs adhere.

8) Bake

Bake 38 to 45 minutes, rotating the pan once at the 25 minute mark. The cake is done when the top is golden, the crumbs are set, and a toothpick inserted in the center comes out with a few moist crumbs but no wet batter. The edges will pull away slightly from the pan.

If using a glass pan: Add a few minutes to the bake time and watch the center closely.

9) Cool and slice

Cool the cake in the pan on a rack for 20 minutes. Use the parchment sling to lift it out. Cool to just warm or room temperature before slicing. This keeps the crumb intact and the blueberries settled.

Nutritional Information (estimate per serving, 12 servings)

• Calories: about 290
• Total fat: about 12 g
• Saturated fat: about 7 g
• Carbohydrates: about 43 g
• Fiber: about 1 g
• Sugars: about 25 g
• Protein: about 3 g
• Sodium: about 180 mg

Values are estimates based on typical ingredients and standard calculators. Actual numbers vary with brands and portion size.

Ingredient Notes and Practical Substitutions

Cake flour vs all-purpose

Cake flour is milled to a lower protein level than all-purpose. Less protein means less gluten development and a finer crumb. That is why this cake stays soft on day two and day three. If you only have all-purpose, you can approximate cake flour by replacing 2 tablespoons of each measured cup of all-purpose with cornstarch, then whisking well, but the result will still be a bit firmer than true cake flour.

Real buttermilk

Cultured buttermilk is milk fermented with lactic acid bacteria. It is tangy, slightly thick, and acidic enough to react with baking soda. That reaction releases carbon dioxide during mixing and early baking, which helps lift the batter. The acidity also keeps the crumb tender.

If you do not have buttermilk, you can use a quick acidified milk by adding 1 tablespoon lemon juice or white vinegar per 1 cup whole milk, then letting it sit 5 to 10 minutes. This gives the right acidity for leavening, but it is thinner and not as flavorful as cultured buttermilk. If your milk is very cold, warm it gently to cool room temperature so it does not seize the butter.

Blueberries

Fresh blueberries work best for clean pockets of fruit. Wash and dry them thoroughly so they do not bleed. If using frozen blueberries, do not thaw. Toss them in flour and fold in gently right from the freezer. Add 3 to 5 minutes to the bake time. Expect a little more color bleeding, which is normal with frozen fruit.

Sugar balance

The batter is lightly sweet on purpose so the crumb topping can carry a bit more sugar and spice. If you prefer a sweeter interior, increase the granulated sugar in the cake by 2 tablespoons. For a lightly less sweet top, cut the brown sugar in the streusel to 2 tablespoons.

Cinnamon and lemon

Cinnamon belongs in the crumb topping. It perfumes the air while the cake bakes and makes the top taste toasty. Lemon zest in the batter is optional but fits the blueberry profile. If you add zest, keep it modest so the buttermilk still shows.

Butter temperature

Cold butter for the crumb makes defined pebbles that stay put. Softened butter in the batter blends smoothly and traps small air pockets during mixing, which helps the crumb stay light. If your kitchen is warm, chill the prepared pan of crumb while you work on the batter.

Technique Tips for a Tender Crumb

• Measure with a scale when possible. The biggest swing in home baking comes from flour packing. A scale gives consistent results and prevents dry, dense cake.
• Avoid overmixing. Once the wet and dry meet, gluten starts forming. Stop as soon as the batter is uniform. The blueberries will finish the last bit of stirring.
• Keep ingredients at compatible temperatures. Butter, buttermilk, and egg at room temp blend faster and reduce the urge to overmix.
• Manage moisture in the fruit. Dry the berries thoroughly if fresh. If frozen, do not thaw, and add a few minutes of bake time.
• Use the middle rack. It gives balanced top and bottom heat so the center sets without a tough crust.

Doneness, Cooling, and Slicing

A toothpick test gives the best signal here. Aim for a few moist crumbs attached, not a smear of wet batter. If the top browns before the center sets, tent loosely with foil in the last 10 minutes.

Let the cake cool for at least 20 minutes before lifting it out. Warm cake slices clean, but still need a gentle hand. For very neat edges, cool to room temperature and cut with a long, sharp knife, wiping the blade between cuts.

Storage, Freezing, and Make-Ahead

• Room temperature: Store the cooled cake in an airtight container at cool room temp for up to 3 days. The crumb topping will soften a bit by day two. A brief warm-up in a low oven brings back some crispness.
• Refrigerator: Not necessary for short storage and can dry the crumb. If your kitchen is hot, chill the cake well wrapped, then bring slices to room temp before serving.
• Freezer: Wrap individual squares tightly in plastic, then in a freezer bag. Freeze up to 2 months. Thaw at room temp. Crisp the crumb by reheating at 325°F (165°C) for 6 to 8 minutes.

To work ahead, make the crumb topping up to 48 hours in advance and keep it chilled. You can also whisk the dry ingredients for the batter a day ahead and store them covered at room temp. Assemble and bake fresh.

Pan Size, Scaling, and Bake Time

• 9×9 pan: Increase ingredients by about 25 percent or live with a thinner cake and reduce the bake time a few minutes.
• 9×13 pan: Double the recipe and bake 5 to 10 minutes longer. Watch the center.
• Muffins: Portion into 12 lined wells, top with crumb, and bake 18 to 22 minutes.

Metal pans give more predictable browning. If you only have glass, keep a closer eye on the center and add a few minutes to the bake.

Troubleshooting

Cake sunk in the center
Likely underbaked or the oven ran cool. Make sure the middle is set before pulling it. Calibrate your oven if it runs cold.

Crumb topping melted into the cake
The butter may have been too soft, or the oven too hot. Keep the crumb cold and the oven at 350°F. If your kitchen is warm, chill the assembled cake for 10 minutes before baking.

Purple streaks in the crumb
That is fruit juice meeting the batter. Dry the berries well and fold them in gently. With frozen berries, do not thaw.

Dry cake
Most often too much flour or overbaking. Use a scale and pull the cake when a toothpick shows moist crumbs. Store covered once cool.

Bitter or soapy taste
This comes from excess baking soda that did not meet enough acid. Stick to the amounts listed and use real buttermilk or properly acidified milk.

The Science In Brief

Baking powder contains both an alkaline component and a dry acid. It activates when wet and again when heated, giving a two-stage rise. Baking soda needs an acid in the batter to react. Buttermilk supplies that acid. The small amount of baking soda here neutralizes part of the buttermilk’s acidity and releases carbon dioxide right away, which helps the fine crumb start forming. Baking powder then continues the lift in the oven, carrying the structure through set. Cake flour’s lower protein means fewer gluten bonds can form, so the crumb stays soft even after cooling. Sugar competes with flour for water and helps keep the cake moist. Butter coats flour particles and limits gluten development, building tenderness into the mix.

Flavor Variations That Still Keep the Texture Right

• Brown sugar batter: Replace 2 tablespoons of the granulated sugar in the batter with brown sugar for a whisper of caramel. Keep the rest the same.
• Nutty crumb: Add 1/2 cup finely chopped toasted pecans or walnuts to the crumb. Stir them in after the butter so they stay craggy.
• Warm spice batter: Add 1/4 teaspoon ground cardamom to the dry ingredients. It plays well with blueberries without taking over.
• Citrus swap: Use orange zest instead of lemon for a rounder citrus note.

Keep changes small. Big shifts in sugar or fat will alter the structure and bake time.

Serving Suggestions

Serve at room temperature or slightly warm. If you want a clean slice for a lunchbox, cool it fully. For an easy dessert, add a spoon of lightly sweetened whipped cream or a small scoop of plain yogurt. In summer, pair a square with fresh berries. In winter, warm a slice on a sheet pan for a few minutes and enjoy the crisped crumb.

Frequently Asked Questions

Can I use frozen blueberries?
Yes. Do not thaw. Toss in a little flour and fold in gently. Add 3 to 5 minutes to the bake time and expect a bit more color bleed.

Can I double the crumb?
You can, but the top may shade the center from heat, which can lengthen the bake and risk a gummy layer. If you like more topping, add an extra 2 tablespoons each of flour and brown sugar and 1 tablespoon butter to the crumb rather than a full second batch.

What if I only have all-purpose flour?
Use it and expect a slightly firmer crumb. For a closer result, for each measured cup of all-purpose, remove 2 tablespoons and add 2 tablespoons cornstarch, then whisk well. Still not identical to cake flour, but closer.

Can I make it dairy free?
You can use a neutral oil for the batter and a plant-based butter for the crumb. Replace the buttermilk with 3/4 cup plant milk plus 2 teaspoons lemon juice or vinegar, rested for 10 minutes. The flavor will differ and the crumb will be a bit less tender.

How do I keep the berries from sinking?
The batter is thick to help suspend fruit. Tossing berries with a small amount of flour gives extra insurance. Very large, heavy berries may still settle a little. That is fine.

Why both baking powder and baking soda?
Baking soda reacts with buttermilk early to start lift and to balance acidity. Baking powder carries the rise through the oven phase. Using both lets the cake rise well without leaving an aftertaste.

How long does it stay fresh?
Up to 3 days at room temp when wrapped or kept in a container. The crumb softens over time, but the cake stays moist.

A Few Oregon-Minded Notes on Fruit and Pantry

Use fresh local blueberries when they are in season. They are firm and tannic enough to keep their shape in the oven and give a true blueberry flavor. If it is off season, frozen berries are a good standby. Keep a small carton of cultured buttermilk in the coldest part of the fridge. Shake it before using since it can separate. If you bake often, store cake flour in an airtight container to keep it from absorbing odors. Measure with a scale and your results will repeat from batch to batch.

Recap

This 8×8 blueberry buttermilk snacking cake is built for dependable texture and clean flavor. Cake flour gives tenderness. Buttermilk and careful leavening make a fine, even crumb. Blueberries deliver pockets of fruit. The cinnamon crumb brings crunch. The method is straightforward, the ingredients are familiar, and the result holds well. It is the kind of bake you make once and then keep in your back pocket for the rest of blueberry season.

Bake it once as written, note your oven’s exact bake time, and you will have a reliable house cake you can count on.