For the crust:
Pulse the flour, sugar, salt and baking powder in the bowl of a food processor until combined. Add half of the butter and pulse until the mixture resembles fine cornmeal. Add the remaining butter and continue pulsing until it is the size of small peas. Add the bourbon and pulse until moistened. Pour in 1 to 2 tablespoons ice water, a bit at a time, until the dough just comes together and holds its shape when squeezed. Turn the dough out onto a large sheet of plastic wrap, gather into a disc and wrap well. Chill until firm, at least 1 hour or overnight.
Preheat the oven to 175°C. Roll out the dough on a lightly-floured surface to an 11-inch circle and fit into a 9-inch pie plate, crimping the edges. Chill to set the crust, 20 minutes.
Prick the bottom and sides of the crust with a fork. Fit the crust with aluminum foil and weigh it down with pie weights or dry beans. Bake until the edge of the crust is just golden, 20 to 25 minutes. Remove the foil and weights and continue to bake until the bottom of the crust is lightly golden and no longer shiny, 10 to 15 minutes longer. Cool completely.
For the filling:
Pour the walnuts and chocolate into the bottom of the cooled crust. Combine the sugar, flour, butter and salt in a small bowl until smooth and set aside. Lightly whisk together the corn syrup, bourbon, vanilla and eggs in a large bowl. Stir together the hot water and baking soda before whisking into the egg mixture. Stir in the flour mixture and then pour over the nuts and chocolate. Bake until the crust is golden and the filling is just set, about 45 minutes. Cool completely on a rack. Serve with whipped cream if desired.