Toasted Oat Rosemary Olive Oil Sourdough Boule

Steps

1. Day 1, about 8 a.m.: feed the sourdough starter equal weights of flour and water and leave it at about 75°F (24°C); it should double and peak in 4 to 6 hours.
2. While the starter rises, toast 80 g of the oats (four-fifths) in a dry skillet over medium heat for 4 to 5 minutes, stirring, until golden and nutty. Pour the 120 g of boiling water over the toasted oats, stir, cover and cool to room temperature to make the oat soaker.
3. About 1 p.m., when the starter has peaked: in a large bowl, mix the bread flour with the 300 g of lukewarm water until no dry flour remains. Cover and rest 30 minutes.
4. Add the sourdough starter, salt, 30 g of the olive oil (three-quarters) and the rosemary to the dough. Squeeze and fold until the oil is absorbed and the dough comes together, about 5 minutes.
5. Add the cooled oat soaker and squeeze it through the dough until evenly spread. The dough is about 70% hydration (not counting the soaker water) and 2% salt.
6. Bulk rise 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, then leave the dough alone until it has grown by about 50%, looks domed and jiggly, and shows bubbles on the sides.
7. Turn the dough onto an unfloured counter, pre-shape into a loose round and rest 20 minutes. Shape into a tight boule.
8. Brush the top of the boule with half of the remaining olive oil (5 g) and roll it in the remaining 20 g of oats to coat. Set it seam side up in a floured basket or towel-lined bowl.
9. Cover and cold proof in the fridge overnight, 12 to 16 hours.
10. Day 2: put a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
11. Turn the boule onto parchment, score the top with a deep slash, and drizzle on the last of the olive oil (5 g). Lower it into the hot Dutch oven.
12. Bake covered for 20 minutes, then uncover, lower to 450°F (230°C) and bake 25 to 30 minutes more, until the crust is deeply browned and the center reads 205°F (96°C).
13. Cool the boule on a rack for at least 2 hours before cutting into 12 slices.