Top any soup with a grilled cheese soup crouton, just like you've seen on French onion soup! Just 3 ingredients: toast, butter, and cheese. Includes video!
Toast the bread. Butter it, then place the two slices of cheese on top of it.
Cooking option A: If you have broiler-safe soup bowls, you can place the heated soup in them, then place the toast with cheese directly on top, then broil for a minute or two until the cheese is melted and has golden brown spots.
Cooking option B: If your bowls are not broiler-safe, place the toast with cheese on top of a baking sheet. Broil for a minute or two until the cheese is melted and has golden brown spots. Place the broiled cheese toast on top of your heated soup.