Creamy Hash Brown Casserole

1/4 cup butter, plus more for dish
1 onion, chopped
1 16oz container sour cream
1 10 1/2oz can cream of celery soup
1 8oz package shredded cheddar and monterey jack cheese blend
1/2 tsp garlic powder
1 30oz package frozen shredded hash brown potatoes thawed
1 tsp salt
1/2 tsp ground black pepper
2 cups crushed potato chips

Preheat oven to 350. Lightly butter a casserole dish.
In a small skillet, melt 1/4 cup of butter over medium heat. Add onions, 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, hash browns, and salt and pepper. Conbine 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.