Sauté onions in butter in a large skillet on low heat until soft.
Add chicken soup; stir. Add sour cream and cheese.
Cook until cheese is melted.
Add salt, pepper, and granulated garlic. Mix in the hashbrowns.
Spray cooking spray in 9x13 casserole dish. Bake uncovered for 45 minutes at 325 degrees. (Like I mentioned above... I usually cook it longer and/or reheat in the oven to make it more golden and crispy around the edges.)