Add all leaven ingredients to a clean, dry quart jar, lightly cover and leave on counter until doubled in size, active and bubbly, 6-10 hours. Add peaked leaven to water in a large mixing bowl. Add flour and stir with a dough whisk until combined into a shaggy dough. Let sit lightly covered for 30 min. before sprinkling salt over dough and combining with damp hands. After dough rests for 45 min., do a series of coil folds with damp hands and continue doing coil folds every 30-60 min. until dough has doubled in bulk and is jiggly. It will probably take 3-4 coil series. Spread up to 2 Tbsp. of water over dough surface before covering bowl with a towel. Place in refrigerator to bulk ferment for 5 hours to overnight. Next, let bowl of dough come to room temperature for 30-40 min. Coat two banneton bowls with rice flour. With damp hands, carefully dump dough onto a clean surface to divide into two halves. Working with one half at a time, laminate dough by gently pulling and stretching out across clean surface. Make it as thin as possible without tearing dough.

Fold dough back onto itself, one corner at a time and push and pull to create tension on dough surface.

Repeat lamination. Place dough, tension-side down, into a floured banneton bowl, cover and chill in refrigerator overnight. Next, preheat oven to 500°F with a Dutch oven (or two Dutch ovens if you want to bake both at once) inside on an air-insulated cookie sheet. Turn one bowl of dough onto a sheet of parchment paper, dust with rice flour and score. Remove and uncover Dutch oven. Lifting by corners of parchment paper, carefully place dough into Dutch oven, replace lid and return to oven. Reduce oven temperature to 450°F and set timer for 25 min. Remove Dutch oven lid, reduce oven temperature to 425°F and bake for additional 25 min. or until nicely browned. Remove from oven and immediately transfer to cooling rack. Wait at least 30 min. before slicing.