
- 1 (14-ounce; 397 g) sheet puff pastry from 1 (17.3-ounce) package, such as Dufour, thawed if frozen; or 1 Pie Dough (i/2 recipe)
- 1/4 cup (60 g) Dijon mustard or an equal-parts mixture of Dijon with crème fraîche (see note)
- 1/4 cup packed grated Gruyere cheese (1 1/2 ounces; 43 g)
- 1 medium tomato (9 ounces; 255 g), cored and sliced 1/4 inch thick
- Kosher salt
- Herbes de Provence, for sprinkling (optional)
- Extra-virgin olive oil, for drizzling
- Preheat oven to 400°F (200°C) and set rack in middle position.
If Using Puff Pastry: On a lightly floured surface, gently roll out the puff pastry until it’s large enough to line an 8- or 9-inch tart pan or a standard 9-inch pie plate, roughly the size of an 10-inch round. Carefully transfer the mixture to a tart pan or pie plate, gently pushing it into the edges, and trim any excess overhang. Dock all over with a fork, then proceed to Step 2.
Pie Dough: for single-crusted pies; Note, you can also use this style of dough for a free-form galette - Spread mustard all over base of tart, then sprinkle Gruyere all over.
- Arrange tomatoes on top of mustard and cheese, then season all over with salt. Sprinkle lightly with herbes de Provence (if using) and drizzle with olive oil.
- Bake until tomatoes are roasted and excess water has cooked off and pastry is browned and crisp all over, about 30 minutes. Let cool slightly, then slice and serve.
- The tart is delicious with plain Dijon. If you want, you can cut it with an equal-parts mixture of crème fraîche, which is also delicious, though by no means necessary.





