Whisk and mix the Rice Flour (6 cup), Sorghum Flour (3 1/4 cup), Tapioca Flour (1 3/4 cup), Potato Starch (1 1/4 cup), and Xanthan Gum (1/4 cup) in a 5 to 6-quart container with a lid.
Finish by picking up the container and vigorously shaking until the flours are completely blended. The ingredients must be very well mixed, otherwise the xanthan gum or psyllium will not be evenly distributed and your loaves will be inconsistent.
In a 5 to 6-quart bowl or stand mixer, whisk together 6 cups of the Gluten-Free Flour Mixture you just made, Instant Dry Yeast (1 tablespoon), Kosher Salt (1 1/2 tablespoon), and Granulated Sugar (2 tablespoon).
Add the Water (3 1/4 cup) and Extra-Virgin Olive Oil (1/4 cup). Mix with a spoon or a heavy-duty stand mixer fitted with the paddle attachment until the mixture is smooth for about 1 to 2 minutes. No kneading necessary.
Cover (not airtight) and allow to rest at room temperature until the dough rises, approximately 2 hours. The dough can be used immediately after the initial rise, though it is easier to handle when cold. Refrigerate in a lidded (not airtight) container and use over the next 7 days. Or freeze for up to 4 weeks in 1-pound portions then thaw in the refrigerator overnight prior to use.
Preheat the oven to 425 degrees F (220 degrees) with an empty metal broiler tray on any shelf that won't interfere with the rising bread. Line a baking sheet with parchment paper.
Dust the surface of the dough and the parchment paper with rice flour or any gluten-free all-purpose flour. Pull off a 1-pound (grapefruit-size) piece. Quickly pat it into a ball on the prepared parchment. Smooth and flatten into a disk by gently pressing with your fingers, until you reach a thickness of 1/2-inch.
For the focaccia with shallots and rosemary: In a skillet, sauté the Shallot (1/4 cup) over medium heat in Extra-Virgin Olive Oil (2 tablespoon) until softened but not browned.
Strew the sautéed shallots over the surface of the dough. Allow some of the dough surface to show through the shallots; you may have some leftover at the end. If you can't see much of the dough surface, you're using too much shallot and your focaccia won't brown attractively.
Sprinkle with Fresh Rosemary (3/4 teaspoon). Season with Coarse Salt (to taste) and Freshly Ground Black Pepper (to taste). Finish with a light drizzle of Extra-Virgin Olive Oil (1 teaspoon).
For the focaccia with olives and rosemary: Strew the Kalamata Olives (1 pound) over the surface of the dough. Allow some of the dough surface to show through the olives. Sprinkle with Fresh Rosemary (3/4 teaspoon). Season with Coarse Salt (to taste) and Freshly Ground Black Pepper (to taste). Finish with a light drizzle of Extra-Virgin Olive Oil (1 teaspoon).
After resting on the prepared baking sheet for 20 minutes, place on a rack positioned in the middle of the oven. Pour 1 cup of hot tap water into the preheated broiler tray and quickly close the oven door to trap the steam. Bake for about 25 to 30 minutes or until the crust is medium brown.
Check the progress after about 20 minutes to be sure the shallots or the edges of the focaccia aren’t becoming overly browned. If they are, cover the loaf or loaves loosely with foil for the remaining time in the oven. The baking time will vary according to the focaccia's thickness. This focaccia will not develop a crackling crust, because of the olive oil.
Allow to cool on a wire rack; then cut into wedges or squares and serve while still warm.