How to Make It
In a food processor, pulse the flour with the sugar and salt. Add the butter and pulse until the mixture resembles coarse meal with some pea-size pieces remaining. Drizzle the buttermilk on top and pulse until the dough just comes together. Turn the dough out onto a work surface, gather up any 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 12-inch round, a scant 1/4 inch thick. Ease the dough into a 9-inch glass pie plate. Trim the overhanging dough to 1 inch, fold it under itself and crimp the dough decoratively. Refrigerate the crust until firm, about 30 minutes.
Preheat the oven to 400°. Line the crust with parchment paper and fill with pie weights or dried beans. Bake the crust in the lower third of the oven for about 20 minutes, until barely set. Remove the parchment paper and pie weights. Cover the edge of the crust with strips of foil and bake for 15 to 20 minutes longer, until the crust is lightly browned. Let cool on a rack. Leave the foil strips on the crust rim. Reduce the oven temperature to 325°.
In a large bowl, whisk the eggs with the sugar until pale. Add the buttermilk, butter, coconut milk, flour, vanilla seeds and both extracts and whisk until smooth, then stir in the shredded coconut.
Set the pie plate on a baking sheet. Pour in the custard and bake for 40 to 45 minutes, until set around the edge but slightly jiggly in the center. Transfer to a rack and let the pie cool completely.
In a small saucepan, combine 1 cup of blackberries with 2 tablespoons of sugar and 1 tablespoon of water. Cook over moderate heat, stirring occasionally, until the berries start to burst. Transfer the berries and any juices to a blender and puree until nearly smooth. Transfer the puree to the saucepan and let cool slightly, then whisk in the cream, blackberry liqueur, vanilla and salt.
In a medium saucepan,combine the remaining 3/4 cup of sugar with 1/4 cup of water. Cook over moderate heat, swirling the pan and brushing down the side with a wetpastry brush, until the sugar dissolves. Cook undisturbed until an amber caramel forms, about 7 minutes. Add the blackberry cream (be careful, it may boil vigorously) and simmer, whisking, until the caramel is smooth, 1 to 2 minutes. Let cool slightly, then stir in the remaining 1 cup of blackberries; let cool to room temperature. Garnish the pie with toasted coconut, cut into wedges and serve with the blackberry caramel.