For levain: In a medium bowl, add 2 tablespoons (33 grams) levain. Add ½ cup (120 grams) lukewarm water. Add flours, and stir thoroughly with spoon or hands until smooth and no dry bits of flour remain. Loosely cover and let stand at room temperature overnight (or 8 to 12 hours before you plan to use).

For dough: In a large bowl, stir together flours. Add 1¼ cups (300 grams) lukewarm water, and stir until a rough dough forms. Knead in bowl until no dry bits remain, 30 seconds to 1 minute. (If dough isn’t coming together after 30 seconds, slowly add remaining 1 tablespoon plus 1 teaspoon (20 grams) water until flour is hydrated but isn’t super sticky. How much water you use will depend on the humidity at the time of mixing. Dough will not be smooth.) Cover and let stand (so flours can hydrate) for 20 to 30 minutes.

Sprinkle dough with salt. Add ½ cup (134 grams) levain. (See note below about what to do with remaining levain.) Using your hand, pinch and squeeze dough (this is not kneading) to help incorporate levain into dough until cohesive and uniform in texture, about 3 minutes. (Dough will not be smooth.)

Cover and let rise in a warm, draft-free place (75°F/24°C), and place a small bowl of water on your workstation. Dipping one hand in water, fold dough every 20 minutes for a total of 4 folds in 1 hour and 20 minutes. (To complete a fold, grab underside of dough, stretch it up, and fold it to center of dough. Do this 4 times around the bowl and then turn dough over so folds are facing down.) (At the end of folding, dough will be smooth and elastic and pass the windowpane test; see Notes.) Let rise until doubled in size, dough jiggles when bowl is tapped lightly, and dough passes finger dent test, 1 to 2 hours. (See Notes.)

For final shape, turn out dough onto a lightly floured surface. Using your fingertips, gently press dough into a 1-inch-thick circle. Stretch out bottom third of circle, and fold to center. Stretch right side out, and fold right third over to center; repeat with left side. Finish by folding top third over previous folds. Roll dough away from you to seam side down, and using both hands, cup dough and pull it toward you to seal. Rotate dough 90 degrees, and pull again until a tight, smooth boule forms, 5 to 7 times. Place, seam side up, in a banneton (proofing basket) or a small bowl lined with a kitchen towel heavily dusted with bread flour. Loosely cover dough with towel, and let rise until puffed, dough jiggles when bowl is tapped lightly, and dough passes finger dent test, 1½ hours to 2½ hours. (Alternatively, cover refrigerate to cold-ferment overnight. Let stand at room temperature for 1 hour before baking.)

Preheat oven to 425°F (220°C). (See How to Bake in a Dutch Oven to bake in a traditional Le Creuset Dutch oven.)

Turn boule out of banneton or bowl onto a round piece of parchment paper. (Alternatively, dust the base of Le Creuset Bread Oven with semolina flour, and turn out dough directly onto base.) Using a lame or sharp paring knife, score top of boule. Place boule, still on parchment paper, in Bread Oven. Cover with lid, and return to oven.

Bake for 30 minutes. Remove lid, and bake until deep golden brown and an instant-read thermometer inserted in center registers 205°F (96°C) to 210°F (99°C), 15 to 20 minutes more. Immediately remove loaf from Bread Oven, and let cool completely on a wire rack.