Mix the flours, cornstarch, yeast, xanthan, and salt on medium low for 1 minute in the bowl of a stand mixer, using the paddle attachment.
Add the water and mix for 4 minutes on medium high. Add the olive and mix for 1 more minute.
Weigh the dough, scrape out into two equal pieces and set each on a 7" square of parchment. Form each dough piece into a ball with wet fingertips, by gently patting to smooth.
Drizzle EVOO over and rub lightly to coat. Set on a baking tray. Cover with cellophane. Seal in a large freezer bag (or cover with another layer of cellophane. Refrigerate for 5-6 hours.
Bring to room temperature 1-2 hours before you are ready to bake. Flour a board with cassava flour. Flatten to 9" by patting gently and making an edge on the outside of the dough.
Slide the dough onto a cornmeal dusted pizza peel. Drizzle with olive oil. Add a scant 1/4 cup of pizza sauce and spread across, leaving the edge without. Top lightly with cheese and toppings.
Bake at 650-700 to start in pizza oven. 2-4 min. Or if using a conventional oven to bake, set the oven to 550 or as high as it goes, with a pizza stone in the oven. Slide the pizza onto the stone once the oven comes to temperature. Bake at 550 13-16 min or until the crust bottom and top are golden brown.