Step 1

Heat a panini grill or a skillet over medium heat. Place the bread on a cutting board and lightly brush the top of each slice with melted butter, being sure to butter all the way to the corners. Turn the slices over and pile Gruyère on 2 of the slices. Place the remaining 2 slices of bread on top of the Gruyère, buttered sides up.

Step 2

Cook the sandwiches on the panini grill or in the pan for about 5 minutes total, flipping once if using a skillet, until nicely browned on the outside and melty and gooey on the inside. Transfer the sandwiches to the cutting board and let rest for 1 minute.

Step 3

Cut the grilled cheese sandwiches into approximately 1-inch croutons. Dunk them into soup, being mindful that if you don't care for soggy grilled cheese, you're going to want to add just a couple croutons at a time to your bowl of tomatoey goodness.