Prep dough: 1. Combine flours, salt and xanthan gum in a large bowl. 2. Cut butter in with two forks or a pastry blender until mix resembles coarse meal. 3. Turn out onto a lightly floured surface and knead until smooth. 4. Form dough into a disk. Wrap in plastic and chill until firm, at least 1 hour. Make: 1. Remove dough from the fridge 5-10 minutes before you begin rolling. 2. Lightly flour your work surface and a rolling pin. 3. Place dough between two large pieces of parchment paper, and roll flat; rolling the dough until 2-3 inches larger than pan you are using and about 1/8-inch in thickness. (If the dough starts to crack, cut a piece of dough from the edge and pat into the crack to patch (you can also add a brush of water to help seal it if needed). 4. To fit dough for a pie pan, fold dough disc in half and lay it across one side of a well-buttered pie pan, positioning seam in center. 5. Unfold disc and gently slide and fit dough down into pan; do not pull or stretch dough. Make sure there are no gaps between dough and pan; if there are air bubbles, burst them with a fork. 6. Trim dough overhang to allow 1-1 1/2 inches excess, measuring from the inner rim of pan. Cover crust with plastic and refrigerate for at least 15 minutes, and tightly wrapped, up to 3 days before using. The rolled out, tightly wrapped crust can also be frozen for up to a month.
To mix dough even quicker with your hands, freeze butter and grate on a box grater, then mix dough together with your hands. If you have a food processor, pulse flours, fats and salt in a food processor until dough begins to clump together, about fifteen 1-second pulses.