Brown the Kielbasa: In a large skillet over medium-high heat, add the sliced kielbasa and cook for 5-7 minutes, stirring occasionally, until the edges are lightly browned and some fat renders out.
Prepare the Cream Cheese Mixture: In a large bowl, whisk together the softened cream cheese, 4 cups of chicken broth, and shredded Cheddar cheese until smooth and well combined, about 2-3 minutes.
Combine Kielbasa and Sauce: Add the browned kielbasa to the cream cheese mixture and stir gently until evenly distributed, then taste and season with salt and pepper as needed.
Prepare the Baking Dish: Preheat your oven to 350 degrees Fahrenheit and lightly grease a 9x13-inch baking dish.
Layer the Pierogies: Spread the thawed or semi-thawed frozen pierogies evenly across the bottom of the prepared baking dish in a single layer.
Pour the Kielbasa Mixture: Pour the creamy kielbasa and broth mixture over the pierogies, gently stirring or shaking the dish to ensure even distribution.
Bake and Finish: Bake uncovered for 25-30 minutes until the sauce bubbles around the edges and the top is lightly golden, then sprinkle with fresh chopped parsley and serve hot.