Adapted from Once Upon a Tart
1 1/4 cups flour
1 1/2 tablespoons semolina flour (1 tablespoon plus 1 teaspoon plus 1/2 teaspoon)
1/2 teaspoon salt
6 tablespoons cold butter, cut into small cubes
1 1/2 tablespoons cold shortening (1 tablespoon plus 1 teaspoon plus 1/2 teaspoon)
2+ tablespoons ice cold water
12 plum tomatoes, cut into 1/4 inch slices, and allowed to drain in colander
1 cup grated Gruyère
1 teaspoon herbes de Provence
1/4 cup half and half
1 teaspoon Dijon mustard
1 teaspoon salt
Freshly ground black pepper to taste
To prepare crust, put flours and salt in food processor and pulse to combine. Add butter and shortening and pulse till mixture looks like cornmeal. Remove to bowl and sprinkle with 2 tablespoons ice water. Mix to combine, and gather together to form ball. If not holding together, slowly add more ice water...avoiding adding too much and forming a sticky dough. Flatten dough ball into a disk, wrap in plastic wrap, and refrigerate at least 30 minutes.
Roll out dough to 1/4 inch thickness and fit into a 9 inch square tart pan (or another tart pan of comparable size), and trimming excess dough. Chill another 30 minutes.
Preheat oven to 400º. Prick bottom of tart with fork, then line with parchment and cover parchment with pie weights or dried beans. Bake for 10 minutes. Remove from oven, then remove paper and weights, and allow to cool as filling is prepared.
Decrease oven temperature to 375º. Sprinkle bottom of tart shell with Gruyère, then herbs de Provence. Top with tomato slices arranged artfully.
Whisk together eggs, half and half, mustard, salt and pepper. Pour over tart, adding more cream if needed.
Bake for 1 hour or longer, till custard is set. Cool on wire rack slightly before serving.