In a food processor, combine flour and salt. Add cold butter and pulse until the size of peas, about 12 times. Add egg yolks and pulse to combine. With the motor running add the ice water and pulse until dough starts to come together. Place on floured surface and roll into a flat disc. Wrap in plastic and refrigerate for 30 minutes.

Preheat oven to 400º and line a baking sheet with parchment paper.

Roll out the dough on a floured surface into an 11 x 17 rectangle and place on the prepared pan. Place a second cookie sheet over the dough to weigh it down while baking. Bake for 15 minutes, remove the top cookie sheet and pierce the dough with a fork. Return it to the oven without the top cookie sheet and bake an additional 8-10 minutes until lightly browned.

While the dough is baking prepare the tomatoes. Slice the tomatoes into ¼ slices and place in a large bowl. In the food processor add basil, thyme, garlic, 1 teaspoon salt and 1 teaspoon pepper and process until finely chopped. Add olive oil and process until combined. Pour over sliced tomatoes and gently toss. Set aside while the dough is baking.

Once the dough has cooled, brush mustard on top and then add ¾ of the gruyere and parmesan. Place sliced tomatoes slightly overlapping on the cheese. Drain the fluid from the tomatoes through a colander and place the herbs and garlic over the tomatoes. Top with remains gruyere.

Bake at 375º for 30 minutes or until cheese is slightly browned. Cool slightly before cutting into squares.