Make the starter: Combine 1,000 grams white-bread flour with 1,000 grams whole-wheat flour. Put 100 grams of warm water in a small jar or container and add 100 grams of the flour mix. Mix until thoroughly combined and let sit at room temperature until mixture begins to bubble and puff, 2 to 3 days.

When starter begins to show signs of activity, begin regular feedings. Keep the starter at room temperature, and at the same time each day discard 80 percent of the starter and feed remaining starter with equal parts warm water and white-wheat flour mix.

Make the leaven: The night before baking, discard all but 1 tablespoon of the mature starter. Mix the remaining starter with 200 grams of warm water and add 200 grams of the white-wheat flour mix. Cover and let rest at room temperature for 12 hours.

Make the dough: In a large bowl, combine 200 grams of leaven with 700 grams of warm water and stir to disperse. Add 900 grams of white-bread flour and 100 grams of whole-wheat flour and mix until no traces of dry flour remain.

Add 20 grams fine sea salt and 50 grams warm water. Use hands to integrate salt and water into dough thoroughly.

Cover dough and let rise for 30 minutes. Fold dough every half-hour for 2 ½ hours more.

Transfer dough to a work surface and cut into 2 equal pieces. Shape into taut rounds and let rest for 30 minutes.

Mix 100 grams whole-wheat flour and 100 grams rice flour. Line two bread-proofing baskets with towels and flour them.

Dust rounds with whole-wheat flour and shape them into smooth balls. Transfer rounds to prepared baskets and let rise for 3 to 4 hours.

Preheat a Dutch oven to 500 degrees. Dust tops of dough with flour mixture, turn one loaf into the pot seam-side down, score the top, cover, and bake at 450 degrees for 20 minutes. Remove lid and bake for another 20 minutes.

Transfer bread to a wire rack to cool for at least 15 minutes before slicing.