Preheat oven to 200 C.
Begin by cutting the puff pastry into six equal rectangles.
Use a paring knife to create a border around each rectangle and poke the center with a fork to prevent it from puffing up.
Arrange the pastry rectangles on a baking sheet.
Brush the edges of each pastry with the egg wash.
Place a layer of Gruyère in the center of each pastry rectangle.
Add the sliced tomatoes on top of the brioche.
Sprinkle sugar over the tomatoes to enhance their flavor.
Season the mixture with salt, pepper, and herbs.
Finish by adding cheese on top.
Bake in the oven for about 25 minutes until the tarts are golden brown and crispy.
