Preparation

• Preheat the oven to 375°F. Spray a 9x13-inch baking dish with cooking spray and set aside.
• In a medium saucepan over medium heat, melt the butter. Whisk in the flour, garlic powder, onion powder, salt, and pepper. Cook for 1 minute.
• Very slowly stream in the milk while whisking constantly. Then stir in mustard. Bring to a simmer while whisking occasionally.
• Once at a simmer, take off the heat, stir in half of the cheese until melted, and set aside.
• Place half of the pierogies on the bottom of the prepared baking dish in an even layer.
• Spread out half of the sauce on top.
• Add half of the sliced kielbasa, followed by half of the sauerkraut.
• Add the remaining pierogies on top, then the remaining sauce, sausage, and sauerkraut.
• Sprinkle all of the remaining mozzarella on the top.
• Cover with nonstick foil or spray a piece of foil with cooking spray and cover the dish. Bake for 60 minutes until bubbly. Remove the foil and bake an additional 15 minutes to brown the cheese.
• Allow to cool slightly and serve.