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