Preparation: Preheat your oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.
Layer the Base: Arrange the frozen pierogies in the bottom of the dish, slightly overlapping if necessary.
Add the Sausage: Scatter the sliced kielbasa rounds evenly over and around the pierogies.
Sauce it Up: In a small bowl, whisk together the condensed soup and sour cream (if using). Pour the mixture over the pierogies and sausage, spreading it to the edges.
Add Cheese: Sprinkle the shredded cheddar cheese generously over the top of the casserole.
Bake: Place in the oven for 25–30 minutes. The casserole is ready when the pierogies are heated through and the cheese is bubbly and starting to brown.
Garnish: Let the dish rest for 5 minutes, then top with sliced green onions before serving.
Menu & Pairing Suggestions
Vegetable Balance: Serve alongside Southern 3-Ingredient Butter Beans or the Oven Baked 4-Ingredient Amish Chicken and Green Bean Bake for a complete meal.
Light Starters: A plate of Southern 4-Ingredient Cucumber Sandwiches offers a cool, crisp contrast to the heavy casserole.
Bread Pairing: Complement the dish with a warm piece of 20-Minute Homemade Bread to catch any extra sauce.
Sweet Finish: Follow this savory meal with a light dessert like Strawberry Jello Cool Whip Pie or the refreshing Slow Cooker Lemon Puff Pastry Pudding.