Preheat your oven to 375 degrees F. Heat oil in a skillet over medium heat. Add the pierogies to the skillet and cook for 2 minutes on each side. Remove from the skillet and set aside.
Cover the pierogi mixture with mozzarella and cheddar cheese. Bake for 12-15 minutes. Once it comes out of the oven, top it off with crispy fried onions.
- If pan-searing the pierogies, fry them in oil for 2 minutes on each side.- Don’t have crispy fried onions? Top the casserole with crushed ritz crackers or scallions.