1 1/4 lb. heirloom tomatoes, cut into 1/4-inch-thick slices
Kosher salt and freshly ground black pepper
1 refrigerated rolled piecrust from a (14.1-ounce) package
2 oz. sharp Cheddar, coarsely grated (about 1/2 cup)
1 tbsp. fresh basil or thyme, plus more for serving
1 large egg
Preheat oven to 400°F. Line a rimmed baking sheet with paper towels. Arrange tomatoes on paper towels and lightly sprinkle with salt; let sit 10 minutes. Blot with paper towels.
Roll piecrust to a 12-inch circle on a piece of parchment paper. Slide paper and crust onto a baking sheet. Top with cheese and basil, leaving a 1 1/2-inch border all around. Season with pepper.
Arrange tomatoes on top of cheese. Fold border of crust over tomatoes. Beat egg with 1 tablespoon water in a bowl; brush on top of crust. Bake until golden brown, 25 to 30 minutes. Let cool for 5 minutes before serving. Serve with additional basil or thyme.