PreparationMake coconut crust: Pulse flour, coconut, sugar, and salt in a food processor several times to mix. Add butter and pulse until most of mixture resembles coarse meal, with remainder in pea-size lumps. Add water and pulse just until mixture forms a dough. (Do not overmix or pastry will be tough.) Flatten dough into a disk, then chill, covered in plastic wrap, 30 minutes. Shape and bake crust: Preheat oven to 350°F. Roll out dough on a lightly floured surface into a 12-inch round, then fit into a 9-inch pie plate. Crimp edge and prick bottom and sides all over. Line shell with foil and fill with pie weights. Bake in middle of oven 15 minutes, then carefully remove foil and weights and bake shell until pale golden, 5 to 10 minutes more. Transfer shell to a rack to cool 5 minutes. Reduce temperature to 325°F. Make filling: Whisk together eggs, sugar, and salt until well blended. Whisk in buttermilk, cornmeal, zest, juice, and nutmeg. Gradually whisk in butter until smooth. Pour filling into pie shell. Cover edge of pie crust with foil to prevent overbrowning . Bake until custard is just set, about 40 minutes. Transfer pie to rack to cool completely. Cooks' note:• Pie tastes best the day it is made.