Place about 10 grams (~2 teaspoons) water in small bowl and set aside. Combine remaining water and levain in large bowl and stir with wooden spoon until levain is mostly dissolved. Add flours and stir until no dry flour remains. Cover and let rest at room temperature for 20 minutes.

Sprinkle salt over dough, add reserved water, and knead gently in bowl until incorporated. Cover and let rest at room temperature for 30 minutes.

Using lightly wet hands, fold dough until tight and uniform, 6 to 8 folds.

Bulk Fermentation: 12 hours at 75˚F, until dough is domed, lightly bubbly, and just doubled in volume. A peek at the underside of the dough along the edges of the bowl should also show a web of fine bubbles. (Do not overproof here—it’s important to shape the loaf as soon as this stage has arrived. That said, there is probably a 1-2 hour window before it’s too late, at least when ambient temps are below 77˚F.)

Dust top of dough lightly with flour and invert onto lightly-floured countertop. Preshape into round and let rest at room temperature for 30 minutes.

Round (or shape however you like, provided you have the banneton and baking vessel to accommodate anything other than a boule) and transfer to floured banneton or lined basket. Cover and let sit for 30 minutes, then transfer to refrigerator for 8 to 24 hours.

One hour before baking bread, adjust oven rack to middle position, set covered heavy-bottomed Dutch oven on rack, and heat oven to 475 degrees.

Lay 12- by 12-inch sheet of parchment paper on counter. Remove loaf from fridge, dust bottom of loaf with flour, and invert onto center of parchment paper.

Carefully remove Dutch oven from oven, place on stovetop, and set lid aside. Using lame or sharp knife held at 30-degree angle to loaf, make series of four 4-inch long, ½-inch deep slashes to form square around perimeter of loaf, about 2 inches in from edge of loaf. (Or score however you prefer.) Pick up dough by lifting parchment edges and lower into Dutch oven. Carefully cover pot and transfer to oven. Bake for 20 minutes.

Remove lid, reduce oven temperature to 425 degrees, and continue to bake until loaf is golden brown, 15 to 20 minutes longer.

Carefully remove pot from oven. Return loaf to bare oven rack and continue to bake until deep golden brown, 5 to 10 minutes longer. Transfer loaf to cooling rack and allow to cool for at least two hours before serving.