Pulse flour, cornmeal, granulated sugar, and salt in a food processor until mixed. Pulse in the butter until the mixture resembles coarse grain.
6 tablespoons ice water, equally drizzled Pulse until the dough stays together when squeezed between your fingers (consistency should not be wet or sticky). If it's too dry, add a tablespoon of water at a time while pulsing.
Form into a disc, cover in plastic wrap, and chill for 1 hour or freeze for up to 3 months.
Combine the apricots, cherries, granulated sugar, cornstarch, and salt in a large mixing basin.
Roll out dough to a 15-inch circle on a lightly floured piece of parchment paper. Fill a 10-inch pie plate halfway with the filling and place the crust on top.
Fold the crust's edges inward, overlapping if necessary. Brush the edges of the dough with egg wash and sanding sugar. Refrigerate for 30 minutes until it becomes hard.
Preheat the oven to 375 degrees Fahrenheit, with racks in the center and bottom. On the lower rack, place a foil-lined baking sheet. Bake for 1 hour and 15 minutes on the middle rack until the crust is brown and the liquids are bubbling in the center. Tent with foil if the crust is browning too soon.
Allow cooling for at least 2 hours before serving on a wire rack. The pie can be kept for up to one day at room temperature.