Maple Oat-Crusted Chia and Flax Sourdough Boule

Steps

1. Day 1, morning: feed your sourdough starter on its usual 1:1:1 feeding (kept separate from this recipe's ingredients) and leave it at about 75°F (24°C) for 4 to 6 hours, until it has doubled, is domed and bubbly, and a spoonful floats in water.
2. Make the soaker while the starter rises: toast the 80 g portion of oats and the sesame seeds in a dry skillet over medium heat for 4 to 5 minutes until golden and fragrant. Tip them into a bowl and add the ground flaxseed, the chia seeds and the maple syrup.
3. Pour the 120 g portion of water, just boiled, over the soaker, stir well, cover and let cool completely, about 1 hour.
4. About 1 hour before the starter peaks, mix the bread flour, the whole wheat flour and the 330 g portion of warm water in a large bowl until no dry patches remain. Cover and rest (autolyse) for 1 hour.
5. Add the 100 g of peaked sourdough starter to the dough and pinch and fold it in for 3 to 4 minutes until fully combined. Rest 20 minutes.
6. Sprinkle the salt over the dough with the final 20 g portion of water and squeeze it through until the dough comes together again. The dough is about 70% hydration (the soaker adds more moisture) and 2% salt.
7. Bulk rise at about 75°F (24°C) for 4 to 5 hours. After the first 30 minutes, spread the cooled oat, chia and flax soaker over the dough and fold it in with a set of stretch-and-folds. Do 3 more sets of stretch-and-folds 30 minutes apart, then leave the dough untouched until it has risen about 50%, looks domed and jiggly, and shows bubbles on the sides.
8. Turn the dough onto a lightly dampened counter, pre-shape it into a loose round and rest 20 minutes uncovered.
9. Shape into a tight boule. Spread the 20 g portion of oats on a plate, mist or brush the top of the boule lightly with water, and roll the top in the oats to coat.
10. Place the boule oat-side down in a banneton or a towel-lined bowl, cover, and cold proof in the fridge overnight, 12 to 16 hours.
11. Day 2: place a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes.
12. Turn the cold boule out onto parchment, oat-side up, and score it with one deep slash or a cross. Lower it into the hot Dutch oven, cover, reduce the oven to 475°F (246°C) and bake 20 minutes.
13. Remove the lid, reduce to 450°F (232°C) and bake 25 to 30 minutes more, until the crust is deeply browned, the oats are toasted and the center reads 205 to 210°F (96 to 99°C).
14. Cool the loaf on a rack for at least 2 hours before cutting into 12 slices.