For the crust:
Cornmeal Crust for a 9-inch single-crust pie, partially prebaked

1 cup unbleached all-purpose flour
¼ cup stone-ground cornmeal
½ teaspoon kosher salt
1½ teaspoons granulated sugar
¼ pound (1 stick) cold unsalted butter, cut into ½-inch pieces
½ cup cold water
2 tablespoons cider vinegar
½ cup ice

For the Filling:

1 tablespoon unbleached all-purpose flour
1 tablespoon stone-ground white cornmeal
¼ cup packed light brown sugar
½ teaspoon kosher salt
5 tablespoons unsalted butter, melted
1 teaspoon vanilla paste (or vanilla extract)
1 cup sour cream
3 large eggs
1 large egg yolk
¾ cup maple syrup (preferably Grade B)
1 cup buttermilk