Mixing and storing the dough:  Whisk together the flours, tapioca starch, yeast, salt and xanthan gum in a 5 quart bowl, or a lidded (not airtight) food container.

Combine the liquid ingredients and gradually mix them with the dry ingredients, using a spoon, a 14 cup food processor (with dough attachment), or a heavy duty stand mixer with paddle, until all of the dry ingredients are well incorporated.  You might have to use wet hands to get the last bit of flour to incorporate if you’re not using a machine.

Cover (not airtight) and allow the dough to rest at room temperature until it rises, approximately 2 hours.

The dough can be used immediately after the intial rise or refrigerate in a lidded (not airtight) container and use over the next 7 days.  The flavor will be best if you wait for at least 24 hours of refrigeration.

On baking day:  use wet hands to take out a 1 pound piece of the dough, about the size of a large grapefruit.  Quickly shape it into a ball.  This dough isn’t stretched because there is no gluten in it – just gently press it into the shape.  You might need to wet your hands a little to prevent the dough from sticking and to create a smooth surface, but don’t use so much water as to make the dough soggy.  Place them each individually on a piece of parchment paper.

Allow the dough to rest, loosely covered with plastic wrap for 90 minutes (40 minutes if you are using fresh, unrefrigerated dough.)

Thirty minutes before baking time:  preheat the oven to 450 degrees with a baking stone placed in the middle rack.  Place an empty metal flat pan on a lower rack.

Just before baking, slash the loaf with a serrated bread knife with a 1/4 ” deep cut.

Transfer the loaf and the parchment paper directly onto the hot baking stone.  Pour 1 C of hot tap water into the metal pan and quickly close the oven door.  Bake for about 35 minutes, removing the parchment paper after 23 minutes of baking so the bottom can brown as well.  Cool on wire racks before slicing.