01 -
Grease the interior of the slow cooker with non-stick spray or a small amount of butter to prevent sticking and ease cleanup.
02 -
Melt the butter in a small saucepan over medium heat. Add diced onions and sauté for 3 to 4 minutes, or until translucent, to enhance flavor.
03 -
In a mixing bowl, whisk together condensed cream of mushroom soup, sour cream, milk, garlic powder, black pepper, and smoked paprika until a smooth sauce forms.
04 -
Arrange half the frozen pierogies in the bottom of the slow cooker. Top with half of the sausage slices, sautéed onions, and shredded cheddar cheese. Pour in half of the prepared sauce. Repeat the layers with remaining ingredients, finishing with a cheese layer.
05 -
Cover and cook on low for 3 to 4 hours or on high for 2 to 3 hours, until the pierogies are tender and cheese is melted and bubbly.
06 -
Sprinkle freshly chopped parsley over the casserole before serving. Serve hot.