For the crust, combine the flour, salt, and sugar in a food processor and pulse to combine. Then, add your optional xanthan gum and butter and pulse 7-8 times until the mixture resembles coarse crumbs. Stream in the ice water one tablespoon at a time while pulsing and then shut off the machine. If the dough holds together when squeezed, it is ready.
Dump the dough out onto a clean work surface and gently knead it into a rounded disk. Wrap in plastic wrap and refrigerate for at least 30 minutes to an hour, or until the filling is ready.
Once chilled, roll out your dough using a rolling pin to about ⅛-inch thick. Roll the dough up the pin and place it into a buttered pie plate, unrolling the dough fully. Crimp the edges and place the crust back in the fridge. You may need to patch some holes or tears in the dough.
Preheat the oven to 375 degrees F.
For the filling, combine the pumpkin, eggs, brown sugar, cornstarch, salt, cinnamon, ginger, and nutmeg.
Then, slowly add the heavy cream and milk and whisk again until everything is well incorporated.
Pour into the prepared chilled pie filling and place in a preheated oven and bake 55-60 minutes, until the crust is browned and the middle of the pie has a slight jiggle.
Remove from the oven and allow to cool completely before serving.
To store, place in the freezer and freeze until solid. Then, wrap in plastic wrap tightly and keep in the freezer until 24 hours before serving. Allow the pie to defrost on the counter or in the fridge.