In a food processor, pulse together 1/4 cup of the pecans, the flour, baking powder and 1/2 teaspoon of the salt. Add the 1/2 cup chilled butter pieces and pulse until coarse crumbs form, about 5 seconds. Drizzle in the ice water and pulse to combine. Wrap the dough in plastic wrap and flatten into a disk. Freeze until firm, about 15 minutes.
On a lightly floured work surface, roll out the dough into a 12-inch round. Transfer to a 9-inch pie plate and cut the excess dough to leave a 1/2-inch overhang. Using your fingers, roll the dough edge under and crimp. Prick the bottom of the pie shell with a fork; refrigerate for 15 minutes.
Preheat the oven to 400 degrees F.
Line the shell with foil and pie weights or dried beans and bake for 15 minutes. Remove the foil and pie weights, reduce the heat to 375 degrees F and bake for another 12 minutes.
Meanwhile, in a heavy-bottomed medium saucepan, whisk together the remaining 5 tablespoons butter and 1/2 teaspoon salt with the coconut sugar, maple syrup and vanilla over medium heat until melted and smooth. Cool the mixture slightly, about 5 minutes. In a medium bowl, whisk the eggs. Whisking constantly, add the sugar mixture into the beaten eggs. Stir in the remaining 2 1/2 cups pecans. Pour the filling into the crust and bake until set, about 25 minutes.
Cool the pie completely before slicing.
In a large bowl, whisk together the rice flour, tapioca flour, potato starch, xanthan gum and salt.
Recipe courtesy of Silvana Nardone