Preheat oven to 350*. Break up chunks of hashbrowns and place in a 9" x 13" casserole dish. Spray top of hashbrowns with cooking spray. Bake for 20 minutes. While hashbrowns are baking, prepare ham and cheese. In a separate bowl, add eggs, cream, milk, onion powder, salt, and pepper. Use an electric mixer and beat for 1 minute. When hashbrowns are done, sprinkle ham evenly on top of hashbrowns, then sprinkle cheese evenly on top of the ham. Pour egg mixture all over and put back in oven for 25 minutes. Pull casserole out and put aluminum foil loosely over top so that it doesn't brown too much. Put back in oven for an additional 15 minutes. Let set for 15 minutes and serve.