Preheat oven to 350. Lightly butter a casserole dish
In a small skillet, melt 1/4 cup of butter over medium heat. Add onion and cook 3-4 minutes, or until soft. Pour mixture into a large bowl. Add the sour cream, cream of chicken soup, cheese, garlic powder, hash browns, salt and pepper. Combine until well blended.
Pour mixture into prepared baking dish and bake for 45 minutes or until hot and bubbly.