Make the crust: Preheat the oven to 350˚. Lightly butter the bottom and sides of a 9-inch fluted tart pan with a removable bottom. Spread the pecans on a baking sheet and toast in the oven, stirring once, 10 minutes; let cool. Set aside 1 cup perfect pecan halves for topping.
Transfer the remaining 1 cup pecans to a food processor with the flour, confectioners' sugar and salt; process until the nuts are finely ground. Add the butter and egg yolk and pulse until the dough is moistened and starts to clump together. Press the dough into the bottom and up the sides of the prepared pan. Freeze until firm, about 20 minutes.
Line the crust with parchment paper or foil and fill with pie weights or dried beans. Bake until firm and dry around the edges, about 25 minutes. Remove the parchment and weights and continue baking until the crust is lightly browned all over, about 15 more minutes. Transfer to a rack to cool completely.
Meanwhile, make the filling: Combine the granulated sugar, golden syrup and water in a medium saucepan over medium-high heat; stir until dissolved. Cook, swirling the pan occasionally, until the mixture turns a deep amber color, thickens slightly and registers 300˚ on a candy thermometer, about 8 minutes. Remove from the heat and stir in the diced butter, 1 piece at a time, until smooth and thickened. Stir in the heavy cream, vanilla and salt. Let cool slightly, stirring occasionally, about 30 minutes.
Pour the filling into the cooled crust and arrange the reserved pecans on top. Refrigerate until cold and set, at least 3 hours or overnight.