Slice tomato thinly and sprinkle with salt to draw out the moisture. Let rest while your balsamic reduces.
1 heirloom tomato, salt
Place your balsamic vinegar into a saucepan over medium-high heat. Bring to a boil then turn down to a simmer. Stir periodically, until vinegar reduces by half, about 7 minutes, then remove from heat.
1/4 cup balsamic vinegar
While your balsamic is reducing, slice rolls in half to create the sandwich. Slice buffalo mozzarella into thin slices.
2 ciabatta rolls, 8 ounces buffalo mozzarella
Once the balsamic is reduced, add the bread with the crust side down to panini maker. Place a layer of mozzarella over it, then tomato slices. Drizzle the balsamic reduction over this. Add the basil leaves next if you choose to use them, then finish with a second layer of mozzarella. Place second slice of bread, crust side up, and close your panini maker.
basil leaves
Cook for 3-5 minutes until the outside is toasted and the mozzarella is melty. Serve immediately.