Broccoli Casserole with Two Cheeses. 2 tablespoons butter. 1 box (10 ounces) frozen chopped broccoli*. 1 medium onion (for about 3/4 cup chopped) 2 large eggs. 1 can (10 3/4 ounces) 98 percent fat-free cream of mushroom soup. 1 cup shredded sharp Cheddar cheese.