Using a stand mixer bowl or a large mixing bowl (if you prefer to cut the butter in by hand), add the millet flour, Ryze Gluten Free Flour MIx, Bob’s 1 to 1 Gluten Free Flour, tapioca starch, and powdered sugar in the stand mixer bowl or other mixing bowl. Mix on low on the stand mixer or stir by hand until combined.
Add butter pieces and mix on medium or cut in the butter by hand with a pastry cutter or two knives until the butter is in small pea sized or smaller pieces. Add egg yolks, vinegar, and milk to the bowl. Mix to combine on medium low speed (or stir together by hand) until the dough starts to come together. Use your hands to press together into a ball.
Divide the dough into two equal pieces. Using a piece of cellophane for each, press each dough ball into a 1 inch thick circle and wrap completely. Refrigerate for 1 to 2 hours (or overnight).
When ready to use, remove from refrigerator. Preheat oven to 400 degrees, with the rack position just above the center of oven.
Roll out the dough, on a parchment piece with flour, and a piece of parchment over the dough, one dough ball for a galette or bottom crust of a two crust pie. Be sure to roll out large enough to leave an overhang over the pie plate for the bottom crust, about 13" for the bottom crust, or 12 - 13" for a galette. Remove the parchment from the top of the crust. Pick the parchment up with the dough stuck to it and invert onto a 9” pie plate or deep dish pie plate for a pie, or a baking stone or round cookie sheet lined with a circle of parchment, for a galette. Pull the top parchment gently off the dough. For a pie, cut around the rolled dough on the outside of the pie plate leaving ½” overhang the edge of the pie crust. For a galette, cut the edges of the outside of rolled out dough to have a smooth edge.