Make the crust: Pulse the flour, granulated sugar, cocoa powder and salt in a food processor. Pulse in 3 tablespoons butter until the mixture looks like cornmeal. Add the remaining 5 tablespoons butter and pulse into pea-size pieces. Pulse in the vodka until the dough clumps together but is still crumbly. If the dough is too dry, mix in the ice water, 1 tablespoon at a time. Turn out the dough onto a piece of plastic wrap; shape into a disk and wrap. Refrigerate until very firm, at least 2 hours or overnight.
Roll out the dough on a lightly floured surface into a 12-inch round. Transfer to a 9-inch pie plate. Fold the overhanging dough under itself and crimp the edges. Refrigerate until firm, at least 1 hour.
Preheat the oven to 350 degrees F. Line the crust with foil and fill with pie weights or dried beans. Bake until the crust looks dry around the edges, about 20 minutes. Remove the foil and weights and bake until dry all over, 10 to 15 more minutes. Transfer to a rack to cool.
Make the filling: Whisk the melted butter, egg, flour and salt in a large bowl until smooth, then whisk in the maple syrup and heavy cream. Pour into the cooled crust and top with the pecans in a decorative pattern.
Carefully cover the edges of the crust with foil. Bake until the filling is set, 55 to 65 minutes. Transfer to a rack to cool completely, about 3 hours.