Serves 4
Pastry Crust
1 1/2 cups all-purpose flour (about 6 3/8 ounces), plus more for work surface
1 teaspoon kosher salt (1/2 teaspoon if using Morton’s kosher salt)
1/2 teaspoon ground turmeric
1/2 teaspoon black pepper
1/2 cup cold unsalted butter (4 ounces), cubed
4 to 5 tablespoons ice water
Tamarind Onions
2 tablespoons canola oil
1 large red onion, thinly sliced into half-moons (about 1 3/4 cups)
1/2 teaspoon kosher salt
1/2 teaspoon black pepper
1 teaspoon crushed red pepper
2 tablespoons tamarind concentrate
Filling
1 1/2 pounds ripe red medium-size and cherry tomatoes
1/2 tablespoon Madras curry powder
1 teaspoon kosher salt, divided
8 ounces low-moisture mozzarella cheese, shredded (about 2 cups)
2 ounces sharp white cheddar cheese, shredded (about 1/2 cup)
1/2 medium red onion, finely chopped (about 2/3 cup)
1/3 cup mayonnaise (such as Duke’s)
1 serrano chile, stemmed, seeded, and finely chopped
1/2 teaspoon crushed red pepper
1 tablespoon olive oil
Pulse flour, salt, turmeric, and black pepper in a food processor until combined. Can also do it by hand. Add butter, and pulse until mixture is crumbly and butter is cut into small bits, about 10 times. Slowly add 4 tablespoons ice water while pulsing, adding up to 1 more tablespoon ice water, 1 teaspoon at a time, until dough comes together and forms a ball. Wrap in plastic wrap, and refrigerate until chilled, about 30 minutes.
Heat canola oil in a large skillet over medium-high until shimmering. Stir in onion, salt, black pepper, and red pepper. Cook, stirring often, until onion is translucent, about 10 minutes. Stir in tamarind concentrate until combined. Remove from heat, and set aside.
Preheat oven to 400°F. Line a large rimmed baking sheet with 2 layers of paper towels. Cut medium-size tomatoes into 1/2-inch-thick slices; cut cherry tomatoes in half. Place tomatoes on paper towels; sprinkle one side with curry powder and 1 teaspoon salt. Let stand 10 minutes.
Stir together cheeses, onion, mayonnaise, serrano, and red pepper in a large bowl. On a floured surface, roll pastry dough into a 12-inch circle or oval, trimming edges, if needed. Transfer dough to a parchment paper–lined baking sheet. Spread cheese mixture over dough, leaving a 2 1/2-inch border around edge. (You may not need all of cheese mixture.) Layer sliced tomatoes, curry side down, on cheese mixture; fill in with cherry tomatoes. Top with tamarind onions. Fold exposed border of dough circle toward center, pleating as necessary. Drizzle tomatoes and onions with olive oil; brush exposed crust with egg.
Bake in preheated oven until filling is bubbling and crust is golden brown, 20 to 25 minutes. Let cool 10 minutes.