2-1/2cupspecan halvescoarsely chop half of them, and leave the rest whole
MAKE THE CRUST
Combine the flour, salt and baking powder in the bowl of a food processor fitted with the metal blade. Pulse a few times to combine. Add the pieces of butter and shortening and pulse until you have coarse crumbs with lots of pea and chickpea-sized clumps of butter and shortening within. Add vodka to the water, then add the water and pulse a few times until the mixture is just evenly moistened and very crumbly. It will not come together into a mass -- that's okay. Dump the crumbly dough out onto a work surface and gather it into a ball. Pat the dough into a 5-inch disc -- don't worry if the edges crack -- and wrap it in plastic. Refrigerate for at least 45 minutes or up to 3 days to rest.
Take the dough out of the refrigerator (if it was in the fridge for a long time, let it sit on the countertop for 10-15 minutes so that it's malleable enough to roll). Dust your work surface lightly with flour and place the dough on top; sprinkle a little flour over the dough. Use your hands to quickly work the dough into a smooth disc -- don't overwork it or warm it up too much, just smooth the edges as best as you can so it's easier to roll. With a rolling pin, roll the dough, turning it frequently and adding more flour as necessary so it doesn't stick, into a 13-inch circle.
Fold the dough into quarters without creasing it and transfer it to a 9-inch deep dish pie pan (the pan should be at least 1-1/2 inches deep).
Gently fit the dough into the pan, easing it inwards rather than stretching it outwards. Don't worry if it tears, just patch it right back up.
Trim the edges to 1/2-inch beyond the lip of the pie pan, if necessary. Turn the edges under to create a rim on the crust (you can use the scraps to patch in any thin areas); then press the rim against the lip of the pan, forming it into an even edge as you go. Using your fingers, crimp the rim. Place the crust in the freezer for at least 15 minutes while you heat the oven.
Preheat the oven to 400°F. Remove the crust from the freezer and place it on a baking sheet (this makes it easy to move in and out of the oven). Cover the crust with a piece of parchment paper and fill it at least halfway full with dried beans or pie weights.
Bake for 20 minutes, or until the crust is pale and partially cooked. Remove the parchment and dried beans/pie weights and set aside while you prepare the filling.
Reduce the oven temperature to 350°F.
MAKE THE FILLING
In a small saucepan over medium heat, melt the butter and cook, swirling the pan occasionally, until the butter smells nutty and is golden brown, 3 to 5 minutes. Once you smell that nutty aroma, take the pan off the heat and pour the browned butter into a large heat-proof bowl to cool. (The milk solids will darken and settle on the bottom of the saucepan. When you transfer the brown butter to the bowl, try to leave as much of this sediment in the pan as possible but don't worry about it too much.)
To the bowl with the brown butter, add the brown sugar, corn syrup, and golden syrup and whisk until smooth. Whisk in the eggs, bourbon, vanilla, and salt.
Sprinkle the pecans in the baked piecrust and then pour the syrup mixture over them. The nuts will float to the top. (It isn't necessary, but for a prettier finished pie, use your fingers to flip over any whole pecans that are upside down, and arrange the whole pecans evenly on the surface.)
Put the pie on the baking sheet (be sure you reduced the oven temperature to 350°F!). Bake until just set and bubbling at the edges, 50-55 minutes. The pie will still wobble just a bit when nudged; that’s okay – it will continue to cook as it cools. Remove the finished pie from the oven and place on a wire rack to cool completely, about 4 hours or overnight. For the neatest slices, use a serrated knife to gently saw through the pecans.