Preheat your oven to 375°F (190°C).

In a large skillet over medium heat, add the sliced kielbasa and cook for about 5-7 minutes until it is nicely browned and slightly crispy. Remove from heat and set aside.

Arrange half of the frozen pierogies in an even layer in a large baking dish.

In a medium bowl, combine the sour cream and cream cheese, mixing thoroughly until smooth. Spread half of this mixture over the layer of pierogies.

Sprinkle the browned kielbasa evenly over the sour cream layer.

Top with the remaining half of the pierogies. Pour the rest of the sour cream and cream cheese mixture over the top, and sprinkle with cheddar cheese.

Cover the baking dish with aluminum foil and bake for 25-30 minutes.

After 30 minutes, remove the foil and broil for an additional 2-3 minutes until the cheddar cheese is bubbly and golden brown.

Let cool for a few minutes, then sprinkle with fresh parsley before serving.