01 - Coat the inside of the Crock Pot with non-stick spray or a small amount of butter to prevent sticking.
02 - Arrange half the frozen pierogi in the bottom of the Crock Pot, followed by half the sliced kielbasa and half the sliced onions.
03 - Repeat with remaining pierogi, kielbasa, and onions to create a second complete layer.
04 - In a mixing bowl, whisk together sour cream, melted butter, cream cheese, garlic, black pepper, salt, and smoked paprika until smooth and fully combined.
05 - Pour the creamy mixture evenly over the layered ingredients in the Crock Pot, then sprinkle shredded cheddar cheese across the top.
06 - Cover and cook on low setting for 4 hours, until pierogi are tender and casserole is bubbly throughout.
07 - Sprinkle fresh chopped chives over the top before serving, if desired.