Combine the millet, sorghum, tapioca, and salt in a medium bowl. Set aside.
120 g millet flour, 120 g sorghum flour, 160 g tapioca flour, 11 g salt
Add the water and sugar to a glass measuring cup. Then add the psyllium husks and stir immediately to prevent clumping. Set aside to let gel for up to 5 minutes.
340 g warm water, 20 g sugar, 20 g whole psyllium husk
Add the starter to the bowl of a stand mixer. Then add the psyllium gel and whisk to combine.
300 g active gluten-free sourdough starter
Add the dry ingredients to the wet ingredients and attach the bowl to the stand mixer. Use the paddle attachment and mix on low speed for 5 minutes or until no dry flour remains in the bowl.
Take the dough out of the bowl and place on your counter. Knead for a few minutes and shape into a smooth round ball. Then place the dough seam side up in a lightly floured 7 inch banneton and put it in a gallon freezer bag.
Let the dough proof at warm room temperature for 45 - 60 minutes (80℉ for 45 minutes in a proofing box works perfectly if you have one).
Transfer the dough to the refrigerator to cold proof for an additional 12-16 hours.
Preheat your oven to 500℉ with a dutch oven or multi cooker inside. Set a timer for 1 hour.
Turn the dough out onto a piece of parchment paper and score as desired with a lame or sharp knife.
Using the parchment paper, lift the dough up and place in the hot dutch oven. Put the lid on and bake as follows:450℉ (lid on) - 35 minutes400℉ (lid off) - 35 minutes350℉ (lid off) - 30 minutesOven off - 10 minutes Take the bread out of the oven and cool completely on a wire rack. Wait at least 4 hours before cutting, but preferably overnight.