Summer Tomato, Mozzarella, and Basil Panini with Balsamic Syrup

Serve with sweet potato chips or a simple green salad.
Bring the balsamic vinegar to a boil in a small saucepan over medium-high heat; cook until 3 tablespoons are left (about 8 minutes).While the vinegar is waning, butter the top half of the bread with the cut side. Sprinkle evenly with basil, cheese and tomatoes. Sprinkle evenly with salt and pepper. Brush the bottom half of the bread with the cut side and a reduced amount of vinegar; place on top of the sandwich. Flip the sandwich over.Preheat a large grill pan over medium-high heat. Brush the mold with cooking spray. Transfer the sandwich to the skillet. Place the sandwich on a cast-iron or heavy skillet and press it lightly until it is flattened. Leave the pan on; cook for 3 minutes on each side, or until the cheese is melted and the bread is lightly browned. Cut the sandwich into 4 equal pieces.