In a medium sauté pan, cook down onions and butter until onions are translucent. Be careful not to brown the onions.
Meanwhile in a large bowl, mix together frozen hash browns, both cheeses, sour cream and cream of chicken, stir well.
Add sautéed onions and butter and mix again.
Spread into a 9 x 13 baking dish.
Sprinkle crush potato chips on top.
Bake in a 350° oven uncovered for 1 hour, or until bubbly.
Let stand 5 minutes before serving. Serves 8-10 depending on how many helpings. They’ll be going back for seconds.