Tomato Cheddar Pie

1 store-bought or homemade pie crust
3 large heirloom tomatoes (about 2 pounds), sliced 1/4" thick
3/4 teaspoon kosher salt, divided
1 cup finely chopped sweet onion
1/2 tablespoon unsalted butter
1 1/2 cups grated sharp cheddar (about 4 ounces)
1/2 cup mayonnaise
1/4 cup coarsely chopped fresh herbs, such as basil, oregano, parsley, and/or thyme 1 teaspoon mild hot sauce
1/2 teaspoon freshly ground black pepper
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Line a rimmed baking sheet with several layers of paper towels. Arrange tomato slices on prepared sheet, sprinkle with 1/4 tsp. salt, and cover with more paper towels. Let drain at least 30 minutes.
Position rack in bottom rung of oven and preheat to 350°F. Line a 9” pie pan with your crust. Trim edges to leave a 1" overhang and crimp as desired. Freeze dough at least 15 minutes.
Line crust with parchment paper or foil and fill bottom with baking beans or weights. Bake crust, rotating halfway through, 20 minutes. Remove weights, pierce bottom of crust all over with a fork, and bake again until very light brown and dry, about 10 minutes more.
Meanwhile, heat a large skillet over medium. Add onion, butter, and 1/4 tsp. salt and cook, stirring occasionally, until onion is softened and just starting to brown, 5–8 minutes. Let cool.
Combine cheese, mayonnaise, herbs, hot sauce, pepper, onion mixture, and remaining 1/4 tsp. salt in a medium bowl. Blot tomatoes with fresh paper towels to remove as much remaining moisture as possible. Arrange tomato slices in pie shell and top with filling; smooth.
Bake pie, rotating halfway through, until golden brown, 40–45 minutes. Let cool to room temperature before slicing.