Add flour and salt to food processor. Add butter and pulse once or twice. Add water a little bit at a time, pulsing twice for a couple of seconds before adding more water. Dough will be shaggy and there should be visible flecks of butter. Turn out onto a lightly floured surface and shape into a disc.
Wrap dough in plastic wrap and chill in the refrigerator for at least 30 minutes. On a lightly floured surface, turn out dough and roll into a 12-inch circle. Lift dough using a rolling pin (if dough is hard to work with, return to the refrigerator to help it firm up a bit) and lay over a lightly greased 9-inch pie plate. Gently press into pie plate and flute the edges.
Beat egg and water with a fork until pale and frothy. Brush egg wash over edges of pie crust. Return to the fridge while repairing the filling.
To make the apple chess filling
Preheat oven to 350°F.
In a large bowl, whisk together sugar, cornmeal, flour, and spices. Add the eggs, milk, melted butter, and vanilla. Whisk until all ingredients are incorporated.
Arrange the sliced apples over the bottom of the prepared pie crust. Pour chess filling over the top.
Place pie pan on a sheet tray and bake for 45 minutes, or until the center just barely jiggles when you tap the pan. Tent with foil halfway through baking to prevent the crust from over-browning.
Let the pie cool completely. Serve with a dusting of powdered sugar or ice cream, if desired.