Preheat the oven to 200 °C top and bottom heat. Cover a baking tray with baking paper.
Cut the baguette about 3 cm deep at a distance of about 2 cm and place it on the baking tray. Cut mozzarella into as many thin slices as there are incisions. Wash and dry the tomatoes, cut out the stem and also cut them into as many slices as there are incisions.
Wash the basil, shake dry, put a few leaves aside for serving, cut the remaining leaves into small pieces and add to the butter. Peel the garlic and also press it into the butter, then season this mixture with salt and pepper and mix evenly with a fork.
Divide the herb butter between the incisions and spread it there, then put 1 slice of mozzarella and 1 slice of tomato in each. Bake the baguette in the oven for about 20 minutes until crispy and the cheese has melted. Remove and serve sprinkled with the basil leaves that have been set aside.