Cheesy Hashbrown Casserole

1 32-ounce package of frozen hash browns
8 oz cooked, diced ham (optional)
2 cans cream of onion soup
1 16 ounce sour cream
2 c shredded cheddar
1 1/2 c Parmesan cheese
 
Preheat oven to 375 degrees
 
In large bowl, mix all ingredients except Parmesan; Spread in greased 9x13 inch pan, sprinkle Parmesan, bake 1 hour.