Parmesan Rosemary Walnut Sourdough Boule

Steps

1. Day 1, about 8 a.m.: feed the sourdough starter equal weights of flour and water from your usual supply and leave it at about 75°F (24°C). It should peak, doubled and bubbly with a domed top, in 4 to 6 hours.
2. While the starter rises, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, cool, and chop roughly. Set the walnuts aside.
3. When the starter peaks, mix the all-purpose flour and the water in a large bowl until no dry flour remains. Cover and rest 30 minutes (autolyse).
4. Add the sourdough starter, salt, olive oil and rosemary to the dough. Squeeze and fold with wet hands for 3 to 4 minutes until evenly combined and smooth. The dough is about 73% hydration and 2% salt.
5. Bulk rise at about 75°F (24°C), covered, for 4 to 5 hours. After the first 30 minutes, do the first set of stretch-and-folds, scattering the walnuts and three-quarters of the Parmesan over the dough as you fold so they are layered through.
6. Do 3 more sets of stretch-and-folds, 30 minutes apart, then leave the dough undisturbed until it has grown about 50%, feels airy, and shows bubbles on the sides and top.
7. Turn the dough onto a lightly floured counter, preshape into a loose round, and rest 20 minutes. Shape into a tight boule and place it seam side up in a floured banneton or towel-lined bowl.
8. Cover and cold proof in the fridge overnight, 12 to 14 hours.
9. Day 2: place a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes.
10. Turn the cold dough onto parchment, score the top with a deep slash, and lower it into the hot Dutch oven. Cover, reduce the oven to 475°F (246°C), and bake 20 minutes.
11. Remove the lid and bake 15 minutes, then sprinkle the remaining quarter of the Parmesan over the top and bake 8 to 12 minutes more, until the crust is deeply browned and the center reads 205°F (96°C).
12. Cool the loaf on a rack for at least 2 hours before cutting into 12 slices.