Preheat oven to 350 degrees Fahrenheit.
Peel and quarter onions.
Coat inside of individual baking dishes with butter.
Fill baking dishes with onions.
Sprinkle 1 TB of grated Parmesan on each dish.
Top with 1 TB of shredded Mozzarella cheese.
Bake at 350 degrees for one hour.
Add more cheese if you want extra melty onions.