Soft Rosemary Oat Rye Focaccia-Style Boule

Steps

1. Day 1, morning: give your sourdough starter its usual feeding (equal weights of fresh feed and water) and leave it at about 75°F (24°C); it should peak, doubled, domed and bubbly, in 4 to 6 hours.
2. About 1 hour before the starter peaks, make the oat soaker: stir the oats into about a quarter of the water (80 g) in a small bowl and let them soak until soft and the water is absorbed.
3. In a large bowl, whisk the honey and the sourdough starter into the remaining three-quarters of the water (250 g) until milky.
4. Add the rye flour, bread flour, salt and rosemary to the bowl and mix with a wet hand or stiff spatula until no dry patches remain; the dough will be sticky and paste-like, as rye dough is. The dough is about 76% hydration (counting the soaker water and the starter's water) and about 2% salt.
5. Rest the dough 30 minutes, then add the soaked oats and three-quarters of the olive oil (30 g) and squeeze them through the dough until the oil is fully absorbed.
6. Bulk rise, covered, at about 75°F (24°C) for 4 hours. During the first 90 minutes, do 3 sets of gentle stretch-and-folds with wet hands, 30 minutes apart; rye dough won't stretch far, so just fold the edges to the center. The dough is ready when it has risen by about half and shows bubbles on the surface.
7. Shape: turn the dough onto a damp counter, fold the edges to the center with wet hands, and cup it into a round boule. Set it seam-side down on a sheet of parchment inside a bowl.
8. Proof 1 hour at about 75°F (24°C), then cover and refrigerate overnight, 12 to 14 hours, until slightly puffed with small cracks on the surface.
9. Day 2: put a covered Dutch oven in the oven and preheat to 425°F (220°C) for 45 minutes.
10. Lift the cold boule out on its parchment. Brush half of the remaining olive oil (5 g) over the top and press a few shallow focaccia-style dimples into it with oiled fingertips.
11. Lower the boule on its parchment into the hot Dutch oven, cover and bake 30 minutes, then uncover and bake 15 to 20 minutes more, until the center reads 205–210°F (96–99°C).
12. Lift the loaf onto a rack, brush it right away with the last half of the remaining olive oil (5 g), and drape a clean towel over it to keep the crust soft.
13. Cool the bread on the rack at least 3 hours before slicing; rye crumb sets as it cools. Cut into 12 slices.