Make the dough: Pulse the flour, cocoa, confectioners' sugar and salt in a food processor until combined. Add the butter; pulse until the mixture looks like coarse meal with pea-size bits of butter. Add the egg and pulse once or twice. (Stop before the dough gathers into a ball.) Turn out onto a sheet of plastic wrap and press into a disk. Wrap tightly and refrigerate until firm, at least 1 hour.
Place the dough on a large sheet of lightly floured parchment paper. Roll into a 12-inch round, no more than 1/8 inch thick. Invert the dough over a 9-inch tart pan with a removable bottom and peel off the parchment; press the dough into the bottom and sides of the pan. (If the dough tears, just pat it back together.) Trim the excess dough. Cover with plastic wrap and chill at least 1 hour.
Position racks in the middle and lower third of the oven; preheat to 350 degrees F. Line the crust with foil, then fill with pie weights or dried beans. Bake on the middle rack, 20 minutes. Remove the foil and weights and continue baking until crisp, 7 to 10 minutes. Transfer to a rack to cool completely.
Prepare the filling: Coarsely chop 1 cup pecans. Combine the butter, granulated sugar, vanilla and kosher salt in a saucepan and bring to a boil over medium-high heat. Cook, stirring, until the mixture turns dark amber, 6 to 8 minutes. Immediately stir in the chopped pecans and cook 1 to 2 more minutes. Remove from the heat and whisk in the corn syrup and brown sugar until dissolved. Cool until lukewarm, then whisk in the eggs and bourbon until combined. (The tart can be made 1 day ahead up to this point; cover and refrigerate the filling and wrap the cooled crust in plastic wrap.)
Increase the oven temperature to 375 degrees F. Place the tart shell on a baking sheet and pour in the filling up to the brim. Arrange the remaining 1/2 cup pecan halves on top. Bake on the lower oven rack until the tart is evenly browned and slightly domed in the center, about 40 minutes. Transfer to a rack to cool completely.