Preheat your oven to 375°F (190°C). Grease the baking dish lightly with butter or non-stick spray to prevent sticking.
Slice the kielbasa into thin rounds and set aside. Mince the garlic cloves to release their aroma.
In a skillet over medium heat, melt a tablespoon of butter and sauté the kielbasa until it’s browned and crispy around the edges, about 5 minutes. Add the minced garlic during the last minute so it becomes fragrant.
While the sausage finishes cooking, take the frozen pierogi and spread them evenly in the prepared baking dish, creating a single layer to ensure even baking.
Spread the cooked kielbasa evenly over the pierogi layer, distributing the crispy pieces for flavor and texture contrast.
In a bowl, mix the sour cream with the shredded cheese and the melted butter, then season with salt and pepper. Stir until smooth and creamy.
Pour the cheese and sour cream mixture evenly over the layered pierogi and kielbasa, covering everything in a creamy coating.
Place the assembled casserole in the oven and bake for 25 to 30 minutes, or until the top is bubbling and golden brown with crispy edges.
Once out of the oven, let the casserole sit for a few minutes to settle, then serve hot, enjoying the melty cheese and crispy pierogi edges with savory slices of kielbasa.
