1. Preheat and Prepare Ingredients

Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with butter or cooking spray.

2. Cook the Kielbasa and Onions

In a large skillet over medium heat, melt the butter. Add the sliced kielbasa and cook for about 5-7 minutes until browned and slightly crispy. Remove from the pan and set aside. In the same skillet, add the diced onions and cook until they become soft and translucent, about 3 minutes. Add the minced garlic and cook for another minute.

3. Cook the Pierogi

While the kielbasa is cooking, bring a large pot of salted water to a boil. Cook the frozen pierogi according to the package instructions (typically about 5 minutes or until they float to the surface). Drain and set aside.

4. Mix the Creamy Layer

In a large bowl, mix together the sour cream, shredded cheddar cheese, smoked paprika, salt, pepper, garlic powder, and onion powder. This mixture will add a rich, creamy texture to the casserole.

5. Assemble the Casserole

Layer half of the cooked pierogi in the prepared baking dish. Spread half of the sour cream mixture over the pierogi, followed by half of the sautéed onions and garlic. Add half of the cooked kielbasa on top. Repeat the layers with the remaining pierogi, sour cream mixture, onions, and kielbasa.

6. Add Cheese and Toppings

Sprinkle the shredded mozzarella cheese evenly over the top of the casserole. For extra crunch and flavor, add the crispy fried onions and crumbled bacon (if using).

7. Bake the Casserole

Cover with foil and bake for 20 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is melted and bubbly.

8. Garnish and Serve

Remove from the oven and let the casserole sit for 5 minutes. Sprinkle fresh parsley over the top before serving. Enjoy warm with a side of sour cream or hot sauce if desired.