How to Make It
In a food processor, pulse the pastry flour with the cornmeal, salt and sugar. Add the butter and pulse until the mixture resembles coarse meal with some pea-size pieces of butter remaining. Sprinkle the water on top and pulse until the dough just starts to come together. Scrape the dough out onto a work surface, gather up the crumbs and pat the dough into a disk. Wrap in plastic and refrigerate until well chilled, about 1 hour.
On a lightly floured work surface, roll out the dough to a 13-inch round, a scant 1/4 inch thick. Ease the dough into a deep 9-inch glass pie plate. Trim the overhanging dough to 1 inch and fold it under itself. Crimp decoratively and chill the crust until firm, about 15 minutes.
Preheat the oven to 375°. Line the crust with parchment paper and fill with pie weights or dried beans. Bake in the lower third of the oven for about 20 minutes, until the crust is barely set. Remove the parchment and pie weights and bake for 20 minutes longer, until the crust is lightly browned; let cool. Increase the oven temperature to 400°.
Poke the sweet potatoes all over with a fork and arrange them on a large, foil-lined baking sheet. Bake for about 1 hour, until tender. Let cool completely, then peel and coarsely mash. Measure out 3 cups of mashed sweet potatoes; reserve the rest for another use.
In a food processor, combine the butter with the granulated sugar and puree until smooth. Add the 3 cups of sweet potato and puree until very smooth. With the machine on, add the eggs 1 at a time until each is just incorporated. Add the coconut milk, cinnamon, ginger, salt and cloves and pulse until no streaks remain.
Scrape the filling into the cooled piecrust. Brush the rim with the egg wash and sprinkle turbinado sugar over the crust and filling. Bake for 45 to 50 minutes, until the filling is just set but slightly jiggly in the center; cover the crust with strips of foil if it gets too dark. Let the pie cool completely, then cut into wedges and serve with unsweetened whipped cream.