In a 4-6 quart crockpot, add three cups of chicken broth, frozen pierogies, sliced kielbasa, and shredded cheddar cheese. Mix well to distribute evenly.
Cook on high for 3-4 hours or on low for 6 hours to allow the flavors to blend.
About 30 minutes before the end of cooking, warm the cream cheese with the remaining cup of chicken broth until smooth.
Pour the cream cheese mixture into the crockpot and stir thoroughly. Sprinkle the remaining shredded cheddar cheese on top. Cover and cook on low for an additional 30 minutes to melt the cheese and blend the flavors.
Serve the casserole hot, and if desired, garnish with sliced green onions for extra color and flavor.
Notes
For a crispy top, broil the casserole in the oven for a few minutes after cooking in the crockpot.