1 1/2 cups (7 1/2 ounces) all-purpose flour
2 teaspoons table salt - divided
10 tbsp. Unsalted butter , cut into 1/2 inch cubes and chilled
6-7 tbsp. Ice water
1 1/2 pounds mixed sliced tomatoes (1/4 inch thick slices
1 shallot, sliced thin
2 tbsp. Olive oil
1 teaspoon minced fresh thyme
1 garlic clove - minced
1/4 teaspoon pepper
2 teaspoons Dijon mustard
3 ounces shredded Gruyerr cheese (3/4 cup)
2 tbsp. Grated Parmesan
1 egg, beaten
1 tbsp. Chopped fresh basil
To make crust:
In food processor, mix flour with 1/2 teaspoon salt. Add butter all at once and pulse about 10-15 times, until mixture resembles coarse crumbs. Transfer to large bowl and sprinkle 6 tbsp. water over the flour mixture. Using rubber spatula, stir and press dough until it holds together. Use extra tbsp. water if necessary. Turn out dough onto lightly floured surface, forming 4 inch diameter disc. Wrap well in plastic wrap and refrigerate for 1 hour.
Dough can be made in advance and refrigerated for up to 2 days or frozen for 1 month.
Slice tomatoes 1/4 inch thick, removing chunks of the gelatinous seed structure if possible. Toss tomatoes with 1 teaspoon salt. Transfer tomatoes to colander and let drain in sink for 30 minutes.
In small bowl, mix together thyme, garlic, pepper, 1/2 teaspoon salt, and olive oil.
Adjust oven rack to lower-middle position and heat oven to 375 degrees.
Line a rimmed baking sheet with parchment paper.
Remove dough from refrigerator and Allow it to soften slightly (about 10 minutes) before rolling.
Shake colander well to rid tomatoes of as much moisture as possible. Place tomatoes in bowl, and mix in sliced shallot and the olive oil mixture mixture.
Roll dough into 12 inch circle on lightly floured parchment paper on firm surface. Transfer dough to parchment covered baking sheet.
Spread dough with Dijon mustard to within 1 1/2 inch of the edge. Sprinkle evenly on top of the mustard with the Gruyere. Shingle tomatoes and shallot evenly over the cheese, trying to let the tomato liquid remain in the bowl.
Carefully grasp 1 edge of dough and fold up about 1 inch over filling. Repeat around circumference of tart, overlapping dough about every 2 inches, gently pleating and pinching to secure. Brush folded edge with egg. Sprinkle Parmesan on top of tomatoes.
Bake until crust is golden brown and tomatoes are bubbling, 45-50 minutes.
Transfer baking sheet to wire rack and allow tart to cool for 10 minutes. Using metal spatula, loosen tart from parchment and carefully slide tart onto wire rack. Let cool to room temperature. Sprinkle with chopped basil. Slice and serve.
