Whole Wheat Walnut Herb Sourdough Boule

Steps

1. Day 1, 8 am: feed your sourdough starter as you usually do (equal weights of fresh whole wheat flour and water, kept separate from the recipe amounts) and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, domed and bubbly; this peaked starter goes into the dough.
2. While the starter rises, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, cool, then chop roughly.
3. About 1 hour before the starter peaks, set aside 10 g of the bread flour for dusting. Stir the whole-wheat flour and the remaining 140 g of bread flour with 360 g of the water (all but 20 g) until no dry patches remain. Cover and rest 1 hour so the whole wheat bran softens.
4. Add the peaked sourdough starter to the dough and squeeze it in with wet hands until even.
5. Sprinkle the salt over the dough with the remaining 20 g of water and squeeze it in. The dough is about 78% hydration (counting the starter) and 2% salt.
6. Add half the olive oil, the thyme, the oregano and the walnuts, and fold and squeeze until the herbs and walnuts are spread through the dough.
7. Bulk rise, covered, at about 75°F (24°C) for 4 to 5 hours. During the first 2 hours, do 4 sets of stretch-and-folds 30 minutes apart: lift each side of the dough and fold it over the middle. The dough is ready when it has grown about 50%, feels airy and shows bubbles at the sides.
8. Dust the counter with half of the reserved bread flour, turn the dough out, pre-shape into a loose round and rest 20 minutes. Dust a basket or towel-lined bowl with the remaining half of the reserved bread flour, shape the dough into a tight boule and set it seam side up in the basket.
9. Cover and proof in the fridge overnight, 12 to 16 hours, until the dough springs back slowly when poked.
10. Day 2: place a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
11. Turn the cold dough onto parchment, score the top, and dimple a few shallow finger-holes around the score, focaccia-style. Brush the top with the remaining half of the olive oil.
12. Lower the boule on its parchment into the hot Dutch oven, cover and bake 20 minutes. Uncover, reduce to 450°F (230°C) and bake 22 to 25 minutes more, until deep brown and crisp, and 205°F (96°C) in the center.
13. Cool the loaf on a rack for at least 2 hours before slicing into 12 slices.