In a bowl of a stand mixer, mix the Ryze flour or gluten free 1 to 1 flour blend, the millet or sorghum, and the tapioca starch, yeast, xanthan (if using), salt, and sugar until well combined. Add the cold water and mix on medium for 3 to 4 minutes. Add the oil and mix for 2 minutes more. Let the dough rest at room temperature for 30 minutes, covered with a towel.
Divide the dough into 3 equal dough balls (using a scale if you have one). Place each ball on a small parchment square drizzled with olive oil. The dough will be soft and a bit sticky. Use wet fingertips to smooth the top of the dough balls, then drizzle olive oil and rub across the top.
Wrap the dough balls in cellophane and Place on small trays (or one larger tray) and wrap the trays in cellophane or seal in a large ziploc bag. Refrigerate at least 3 hours, but preferably not more than 24 hours before using.
Let come to room temperature for 1 hour before making pizza or flatbreads. When ready to proceed, flour a board and press the dough into a 9 1/2 or 10" circle for each pizza.
Preheat a pizza stone or baking stone in the oven at 450 degrees. When the stone is preheated, sprinkle with cornmeal, and slide the crust onto the stone. Poke holes in the crust with a fork. Prebake for 8 - 9 minutes or until slightly golden. Add a drizzle of olive oil, sauce, and pizza toppings and bake for 8-10 minutes more or until browned to your liking.