Line the bottom of a loaf pan with parchment paper.
In a large bowl, combine all of the levain, water, olive oil and psyllium husk. Immediately whisk in the psyllium and let it gel for 5 minutes. Then addd the brown rice flour, almond flour, millet flour, tapioca starch, salt, sugar and hemp seeds (if using)
Mix the dough well by hand, or with a kitchen mixer fitted with a dough hook running at medium-low speed, until all the ingredients are completely combined.
Dust some brown rice flour onto a clean surface and knead the dough for a couple of minutes and shape it into a lot the size of your loaf pan.
Place the dough in a warm location and let it rest at for 2-5 hours. The proofing time depends on the temperature in your house.
Preheat the oven to 425°F (218°C). Place the loaf pan inside and bake for 25 minutes. Reduce the heat to 400°F (204°C) and bake for 35 to 40 minutes
Cool the sourdough for 20 minutes before removing from the pan and then cool the bread for at least 2 hours before cutting.
Slice and freeze half of the loaf and keep the rest covered and on the counter for 3 or 4 days.