Brown Onions In Butter For 10 Minutes. Add Broth And Bay Leaf. Season With Salt And Pepper. Cover And Simmer For 30 Minutes. Remove Bay Leaf. Pour Soup Into Ovenproof Casserole Dish. Cover With Bread Slices. Sprinkle With Cheese And Bake In 400 Degree Oven Until The Cheese Has Browned. Serve.