Mix cheeses together. Grease a 9 by 13-inch pan and place half of the cheese on the bottom of the ungreased pan. Melt the butter and saute the mushrooms, onions, and bell pepper and cook until tender. Put the sauteed vegetables over the cheese in the pan. Sprinkle the spinach or ham on this layer. Sprinkle the rest of the cheese on this layer. Cover with plastic wrap and place in the refrigerator overnight.

In the morning, preheat the oven to 350 degrees. Beat the eggs until smooth, add the flour and milk, continue beating. Pour this mixture over the casserole above after removing the plastic wrap. Bake uncovered for 45 minutes, until set and browned. Let it sit for ten minutes before serving.