Combine cream of mushroom soup, sour cream, 1 cup of shredded cheese, and 1 cup of French Fried Onions in a pan over medium heat. Stir together until heated through and well mixed.
Cook frozen broccoli according to package instructions, drain and set to the side until cream of mushroom soup is heated through.
Mix broccoli into the cream of mushroom soup mixture until well coated.
Pour broccoli mixture into a greased baking dish. Bake uncovered for 20-25 minutes.
Remove from oven, cover with remaining shredded cheese and French fried onions. Bake an additional 10-15 minutes until cheese is melted.