Ensalada Caprese is a classic Italian dish, and this recipe transforms it from a simple, boring, grilled cheese to one of the best sandwiches you'll find!
Slice tomatoes into medium slices (should have about 12 slices for 4 sandwiches, or 3 slices per sandwich), and place them in a shallow dish. Pour 2 Tbsp balsamic vinegar over tomatoes. Let sit while preparing the remainder of ingredients.
Butter both sides of bread lightly. Turn over, so butter is facing down. Top 1 slice with 1 Tbsp of Pesto, add 1 Slice of cheese, 3 tomatoes, and then another slice of cheese. If you like it really pesto-y, add some more pesto to top slice. Drizzle just a little bit of balsamic and sprinkle with salt and pepper before placing top bread slice butter side out.
Heat skillet or panini press, and put sandwich on to cook. If using a skillet, about 3 minutes per side.