Rosemary Walnut Rye Sourdough Boule

Steps

1. Day 1, morning: feed your sourdough starter as you usually do (equal weights of fresh feed and water) and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, bubbly and domed at its peak.
2. While the starter rises, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, then cool and chop them. Set aside 10 g of the bread flour for shaping.
3. When the starter peaks, stir the sourdough starter into the water in a large bowl, then add the rye flour and the remaining 140 g of bread flour and mix until no dry patches remain. Cover and rest 30 minutes.
4. Sprinkle the salt over the dough, add 20 g (four-fifths) of the olive oil and the rosemary, and squeeze and fold with wet hands until absorbed. The dough is about 80% hydration (counting the starter) and 2% salt.
5. Bulk rise at about 75°F (24°C) for 4 hours. After the first 30 minutes, add the walnuts during the first set of stretch-and-folds, then do 2 more gentle sets 30 minutes apart, keeping your hands wet since rye dough is sticky. Bulk is done when the dough has grown about 50% and looks puffy with bubbles at the edges.
6. Dust the counter with half of the reserved bread flour, turn out the dough, and shape it into a tight round boule. Dust a banneton or towel-lined bowl with the remaining reserved bread flour and set the boule in it seam side up.
7. Cover and cold proof in the fridge for 12 to 14 hours overnight.
8. Day 2: put a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
9. Turn the boule onto parchment, brush it with the remaining 5 g of olive oil, and score a cross on top.
10. Lower it into the hot Dutch oven, cover, and bake 25 minutes. Uncover, reduce to 450°F (230°C), and bake 20 to 25 minutes more, until deep brown and 205°F (96°C) in the center.
11. Cool the loaf on a rack for at least 3 hours, since rye crumb sets as it cools, then cut into 12 slices.