Adapted from the Kosher Palette

Ingredients
2 eggs, lightly beaten
½ cup milk
½ cup mayonnaise
1 small onion, chopped
1 ½ packages (15 total ounces) frozen chopped spinach, thawed and drained
2 cups sliced mushrooms, sautéed in 2 Tablespoons oil
3 tablespoons flour
1 cup shredded cheddar cheese
1 cup shredded mozzarella cheese
3 tablespoons shredded Parmesan cheese

Preparation
Preheat oven to 350 degrees
Combine eggs, milk, mayonnaise, onion, spinach, mushrooms, flour, ¾ cup cheddar cheese, and ¾ cup of the mozzarella cheese.
Pour into a greased 9-inch round or glass pie plate. Sprinkle with remaining cheese and Parmesan cheese.
Bake 30 – 45 minutes or until puffed in center.