Tomato and Gruyère Tart

1. Prepare the dough

Process the all-purpose flour and 0.5 teaspoon of table salt in a food processor for about three seconds. Add the chilled butter pieces and pulse the mixture until it resembles coarse crumbs, which should take about ten pulses. Transfer this mixture to a large bowl. Sprinkle in the ice water, beginning with 6 tablespoons and adding up to 1 tablespoon more if needed, stirring and pressing with a rubber spatula until the dough comes together and sticks. Form the dough into a disk, wrap it in plastic wrap, and refrigerate it for at least one hour.

2. Prepare the tomatoes

While the dough is chilling, toss the sliced tomatoes with 1 teaspoon of table salt in a large bowl, then transfer them to a colander set over the bowl to drain for about 30 minutes.

3. Preheat the oven

Preheat your oven to 375 degrees Fahrenheit and line a rimmed baking sheet with parchment paper.

4. Roll out the dough

On a lightly floured counter, roll the chilled dough into a 12-inch circle and carefully transfer it to the prepared baking sheet. It’s fine if the dough runs up the lip of the sheet slightly.

5. Prepare the filling

In a now-empty bowl, combine the drained tomatoes with the sliced shallot, extra-virgin olive oil, fresh thyme, minced garlic, black pepper, and the remaining 0.5 teaspoon of table salt.

6. Assemble the tart

Spread the Dijon mustard evenly over the dough, leaving a 1.5-inch border around the edges. Sprinkle the Gruyère and Parmesan cheeses over the mustard. Arrange the tomato mixture over the dough in concentric circles, maintaining the 1.5-inch border. Fold the edges of the dough over the filling, overlapping and gently pinching every 2 inches to secure. Brush the folded edges with the lightly beaten egg.

7. Bake the tart

Bake the tart in the preheated oven for 45 to 50 minutes, until the crust is golden brown and the tomatoes are bubbling.

8. Cool the tart

Once baked, transfer the tart to a wire rack using a metal spatula to loosen it from the parchment paper. Allow it to cool on the sheet for 10 minutes, then transfer it directly to the rack to cool for an additional 20 minutes. Once cooled, sprinkle the tart with the chopped fresh basil, cut it into slices, and serve.