Preheat your oven to 375°F.

In a large pot, bring water to a boil and add a generous amount of salt.

In a skillet, melt the butter over medium heat. Add the kielbasa and cook for about 5 minutes until golden brown. Remove and set aside.

Add the bacon to the skillet and cook for another 5 minutes until crispy. Remove, leaving 2 tablespoons of fat in the pan.

Add the chopped onions to the bacon fat and cook until slightly golden, about 5 minutes.

Add the pierogi to the boiling water in batches. Cook until they float, then boil for an additional minute. Remove with a slotted spoon.

Lightly oil or spray a baking dish. Layer the cooked pierogi in the dish, then top with half of the sausage, bacon, and onions.

Mix the mushroom soup with 1.5 cups of milk until smooth. Pour half over the first layer of pierogi.

Add a second layer of pierogi, then spread the remaining sausage, bacon, onions, and mushroom soup over it.

Sprinkle evenly with shredded cheese. Cover and bake for 15 minutes.

Remove the foil and bake uncovered for an additional 15-20 minutes, until the cheese is bubbly and golden.

Serve hot with a dollop of sour cream. Enjoy!