Easy Key Lime Dump Cake: A Potluck Dessert for 12

One-Pan Key Lime Dump Cake for 12

A 9-by-13-inch pan of key lime dump cake is easy to carry to a potluck and simple to serve. This version makes 12 generous portions, with a tart, creamy lime layer beneath a soft cake topping. You’ll need one mixing bowl for the filling, but the dessert is assembled and baked in a single dish.

The name “dump cake” describes the assembly: spread the filling in the pan, scatter dry cake mix over it, and add butter before baking. You don’t stir the layers together. The butter and moisture from the filling turn the cake mix into a topping that is tender in places and lightly crisp at the edges.

Key Lime Dump Cake Recipe

Yield: 12 servings
Prep time: About 15 minutes
Bake time: 45 to 55 minutes
Cooling time: At least 1 hour
Pan: 9-by-13-inch (23-by-33-cm) baking dish

Ingredients

For the lime filling:

• 2 cans (14 ounces or 397 g each) sweetened condensed milk
• 4 large egg yolks
• ¾ cup (180 ml) bottled key lime juice or freshly squeezed lime juice
• 1 tablespoon finely grated lime zest, optional

For the topping:

• 1 box (about 15.25 ounces or 432 g) yellow or white cake mix
• ¾ cup (170 g) unsalted butter, melted

For serving, optional:

• Whipped cream
• Thin lime slices or a little extra lime zest

Use sweetened condensed milk, not evaporated milk. The two products behave differently, and evaporated milk will not make the same filling. Bottled key lime juice is convenient and gives a consistent tart flavor. Fresh Persian limes also work; the dessert will still be a lime dump cake, though its flavor will differ slightly from one made with key limes.

Instructions

1. Heat the oven and prepare the pan. Set the oven to 350°F (175°C). Lightly grease a 9-by-13-inch baking dish.

2. Mix the filling. In a large bowl, whisk the sweetened condensed milk and egg yolks until smooth. Whisk in the lime juice and zest, if using. Pour the mixture into the prepared dish and spread it evenly.

3. Add the cake mix. Sprinkle the dry cake mix over the filling in an even layer. Do not stir. Break up any large clumps with your fingers or a fork.

4. Add the butter. Slowly drizzle the melted butter over the cake mix, covering as much of the surface as possible. Check for large patches of dry mix and spoon a little butter over them if needed. A few small dry-looking spots are fine.

5. Bake. Place the dish on the center oven rack and bake for 45 to 55 minutes. The topping should be golden in spots, and the filling should be set around the edges. The center may still have a slight wobble when the pan is gently moved, but it should not look liquid. If the top browns too quickly, loosely cover the dish with foil for the remaining bake time.

6. Cool and chill. Let the cake cool on a rack for at least 1 hour. For neater portions and a firmer filling, cover and refrigerate it for at least 2 hours before serving. Cut into 12 pieces and add whipped cream or lime zest just before serving, if you like.

What to Expect From the Texture

This dessert does not slice like a layer cake. The lime filling is soft and creamy, and the topping varies across the pan: some bites are tender where the cake mix meets the filling, while the buttered surface has firmer, golden patches. Chilling helps the filling hold together, but a serving spatula is more useful than a cake server for lifting portions.

The dry cake mix needs reasonably even coverage from the melted butter. Pouring all the butter into one area can leave powdery patches elsewhere. You don’t need to soak every grain, and you shouldn’t stir the topping into the filling. Just spread the mix evenly and drizzle the butter slowly across the whole pan.

A glass or ceramic baking dish makes it easy to see when the filling has set near the edges. If you use a metal pan, begin checking at the early end of the bake-time range. Ovens and pans vary, so the appearance of the filling and topping is a better guide than the clock alone.

Making It for a Potluck

For a dessert for 12, cut the pan into three rows by four rows. The portions are generous, especially if other sweets are on the table. A small offset spatula or flexible serving spatula helps lift the first piece; after that, serving gets easier.

You can bake the cake the day before a gathering. Cool it, cover it, and refrigerate it overnight. Keep it chilled during transport, particularly in warm weather, and return leftovers to the refrigerator promptly. Because the filling contains eggs and dairy, don’t leave the pan at room temperature for more than 2 hours, or more than 1 hour if the temperature is above 90°F (32°C).

Wait to add whipped cream until serving time. It travels better separately, and guests can choose how much they want. The cake is good cold, which also makes it convenient when oven space is scarce at a family meal.

Storage and Small Adjustments

Cover leftovers tightly and refrigerate them for up to 3 days. The topping softens as it sits, though the lime flavor remains bright. Freezing is possible, but thawing can change the texture of the creamy filling, so refrigeration is the better choice when you’re making it only a day or two ahead.

Yellow cake mix gives the topping a buttery, familiar cake flavor. White cake mix keeps the lime more prominent. Either works with the same method. If you use salted butter, the dessert will have a slightly saltier finish; there is no need to add extra salt.

Lime zest adds aroma without making the filling much more sour. Grate only the green outer layer of the peel, stopping before the bitter white pith. If you’re using bottled juice and don’t have fresh limes, leave the zest out. The filling already has enough lime juice to give the dessert its tartness.

A Pan Dessert That’s Easy to Share

This key lime dump cake is best made ahead, chilled, and served straight from its baking dish. The 9-by-13-inch pan yields 12 portions without any stacking or decorating, and the soft filling makes a pleasant contrast with the golden cake topping. Bring a spatula, keep the pan cold until serving, and let everyone help themselves.