To make this dish ahead of time, follow the instructions through #3. Cover with foil and put in the refrigerator for up to 24 hours. When ready to bake, preheat your oven to 350 degrees. Top with 1 cup cheddar cheese and fried onions. Bake covered for 30 minutes. Remove the foil and continue baking for 20 minutes or until the cheese is melted and the casserole has begun to brown around the edges.