Feed the starter: 4-6 hours before baking, feed your gluten-free sourdough starter until bubbly and doubled.
Mix dry ingredients: In a large bowl, whisk brown rice flour, buckwheat flour, tapioca starch, and psyllium husk powder.
Combine wet ingredients: In another bowl, mix warm water, honey, olive oil, apple cider vinegar, and active starter.
Form dough: Pour wet ingredients into dry. Stir until a sticky dough forms. Add salt and mix for 1 minute.
First proof: Cover and proof for 8-12 hours at room temperature (68-75°F/20-24°C) until slightly airy.
Shape dough: On a floured parchment, shape into a round loaf, tucking edges underneath.
Second proof: Place in a floured proofing basket and proof for 2-4 hours until slightly puffy.
Preheat oven: Heat oven to 450°F (230°C) with a Dutch oven inside for 45 minutes.
Bake: Transfer dough to a hot Dutch oven, score the top, and bake covered for 30 minutes. Uncover and bake 15-20 minutes until golden.
Cool: Cool on a wire rack for 1 hour before slicing.
