Layer in an 8x13 pan, in this order:
1 bag hash browns (large cut)
1 small onion, chopped
1 can cream of mushroom soup
1 250 mL tub sour cream
Bake at 350 about half an hour. (Scientific, I know.) Then top with 2 cups grated cheddar, then with crushed Corn Flakes, about 1 cup, and then 1/2 cup melted butter. (Trust me!) Bake again for about 15 minutes.
If you're feeling lazy, you can throw all the layers on at once and bake 40 minutes.
This one's great for showing off at pot lucks, or serving up at a barbecue.