Tomato-Cheddar Pie

kosher salt

sugar

all-purpose flour, plus more for surface

cold unsalted butter, cut into cubes

large heirloom tomatoes (about 2 pounds), sliced 1/4" thick

kosher salt, divided

All-purpose flour (for surface)

finely chopped Vidalia onion (about 1/2 medium onion)

unsalted butter

grated sharp cheddar (about 4 ounces)

mayonnaise (preferably Duke's)

coarsely chopped fresh herbs, such as basil, oregano, parsley, and/or thyme

mild hot sauce

freshly ground black pepper

9" pie pan