Thoroughly mix millet flour, psyllium fiber, sorghum, brown rice flour and yeast in the bowl of a stand mixer. Add starter mixture. On low speed with the dough hook attachment, slowly add honey, warm water and add egg whites. The dough will be sticky, but not wet or dry. Knead on medium speed in your mixer for 5 minutes. Allow to rest 10–15 minutes in the mixer, then add salt and baking powder. Knead again for a few minutes, making sure the mixture is well blended.
Place dough in an oiled bowl and cover with a towel. If you want to bake your pizzas later, place the dough in the fridge for a slow rise. If you are baking sooner, either leave in a warm draft free place, or place in the oven with the light on. Allow to rise until doubled in size. This will take 1–2 hours, depending on how warm your area is. The oven only takes about an hour.
When ready to bake, preheat oven to 450°F. Line a baking sheet with parchment paper lightly dusted with cornmeal. Divide dough into two equal pieces. Roll into a ball, then flatten with wet hands into the shape you desire. Bake for 5 minutes. Top as you like and bake for an additional 10–15 minutes, or until your cheese is browned and bubbly and your crust is golden brown. Repeat with remaining dough and enjoy!
