Dough Pulse flour, cocoa, powdered sugar and salt in a food processor until combined. Add butter, pulse until mixture looks like coarse meal. Add egg and pulse twice, stop before dough gathers into a ball. Turn out onto a sheet of plastic wrap and press into a disk. Wrap tightly and refrigerate until firm, 1 hour.
Place dough on a large sheet of floured parchment paper. Roll into a 12" round, no more than 1/8" thick. Invert dough over a 9" tart pan with a removable bottom and peel off parchment, press dough into the bottom and sides of pan. Trim excess dough. Cover with plastic wrap and chill 1 hour.
Heat oven to 350°. Line crust with foil, then fill with pie weights or dried beans. Bake 20 minutes. Remove foil and weights and continue baking until crisp, 10 minutes. Transfer to cool completely.
Filling Coarsely chop 1 cup pecans. Combine butter, sugar, vanilla and salt in a saucepan and bring to a boil. Cook until mixture turns dark amber, 8 minutes. Stir in pecans and cook 2 more min. Remove from heat and whisk in corn syrup and brown sugar until dissolved. Cook until lukewarm, then whisk in eggs and bourbon until combined.
Increase oven temp to 375°. Place tart shell on a baking sheet and pour in filling. Arrange remaining pecan halves on top. Bake until tart is browned and slightly domed in the center, 40 minutes.
Transfer to cool completely.
Prep times includes chilling times.
Cook times includes time for the crust, then times for the tart itself.
Remember, cooking times may vary depending on ovens, so test doneness before stated cooking times.