You can bake pierogi without thawing in a kielbasa casserole. A little extra liquid and a covered bake help them cook through; uncover the dish at the end to brown the cheese.
Essential Concepts
No boiling needed. Keep covered until tender.
Related posts: [How to Cook Frozen Pierogi](/how-to-cook-frozen-pierogi/) and [Kielbasa Casserole Ideas](/kielbasa-casserole-ideas/).