Prepare the Crockpot: Spray the inside of your slow cooker with non-stick cooking spray to prevent sticking. Set the slow cooker to low heat while you get your ingredients ready.

Layer the Pierogi: Start by layering half of the frozen pierogi evenly across the bottom of the crockpot.

Add Kielbasa and Onion: Next, add half the sliced kielbasa uniformly over the pierogi, followed by half of the chopped onion.

Mix the Creamy Base: In a separate bowl, combine the condensed cream of mushroom soup, sour cream, and melted butter, stirring until smooth.

Repeat the Layers: Now, repeat the layering process using the remaining pierogi, followed by the rest of the kielbasa and onions.

Cover and Cook: Cover the crockpot with its lid and set it to cook on low for 4 to 5 hours.

Add Cheese: During the last 30 minutes of cooking, sprinkle the shredded cheddar cheese over the top of the casserole.

Serve and Garnish: Once cooked, gently stir the casserole before serving warm. Sprinkle with chopped chives to add a burst of color and freshness.