1 recipe unsweetened pastry for a 9-inch single crust pie
1/2 cup grainy brown mustard
3 large ripe tomatoes, thinly sliced
6 slices Swiss cheese, about 1/4-inch thick
1 tablespoon olive oil, or as needed
2 tablespoons herbes de Provence
Preheat oven to 375 degrees F (190 degrees C). Fit the pie crust into a 9-inch pie dish. With a fork, poke holes into the bottom of the crust.
Spread the mustard over the bottom of the pie crust in an even layer. Cover the mustard with the Swiss cheese in a layer. Arrange slices of tomato, overlapping in a spiral from the edge to the center, covering up the cheese. Drizzle olive oil over the tomatoes, and sprinkle the tart with the herbes de Provence.
Bake in the preheated oven until the crust has browned, the cheese has melted, and the tomatoes are curled at the edges, about 20 minutes.