As soon as tomato season starts, it's impossible to resist this summer tart! A classic in France - but still too little known elsewhere - it's all about simplicity: a thin layer of mustard, melting cheese, beautiful ripe tomatoes and crispy pastry. The little secret: the quality of the tomatoes makes all the difference. Never put them in the fridge! Use only sun-drenched, fragrant tomatoes, and they'll turn this simple tart into a real speciality. Served hot with a green salad or cold at a picnic, it's perfect for any occasion.