Toasted Oat Spelt Cheddar Seeded Boule

Steps

1. About 12 hours before mixing, feed your sourdough starter equal weights of whole spelt flour and water from your own starter supply (separate from this recipe's spelt flour), and leave it at about 75°F (24°C). It should peak, doubled and bubbly, in 4 to 8 hours; use it at or just after its peak.
2. Toast half of the oats in a dry skillet over medium heat, stirring, until golden and fragrant, about 4 minutes. Tip into a bowl, add the flaxseed and 100 g of the water, and soak 30 minutes into a thick soaker.
3. In a large bowl, stir the whole spelt flour and 90 g of the bread flour with 240 g of the water until no dry patches remain. Cover and rest 30 minutes (autolyse). Set the remaining 10 g of bread flour aside for dusting.
4. Add the sourdough starter, maple syrup, salt and the remaining 20 g of water to the dough, and squeeze and fold until fully combined, about 3 minutes. The dough is about 73% hydration and 2% salt (soaker water included).
5. Add the oat-flax soaker and squeeze it through the dough until evenly mixed. Cover and begin the bulk rise at about 75°F (24°C).
6. Over the first 2 hours, do 4 gentle sets of stretch-and-folds, 30 minutes apart. On the second set, scatter the cheddar cubes over the dough and fold them in.
7. Let the dough rest undisturbed another 2 to 3 hours, until risen about 50%, domed and airy at the edges, and jiggly when the bowl is shaken (4 to 5 hours of bulk in all).
8. Mix the remaining untoasted oats with the sesame seeds on a plate. Dust the counter with half of the reserved bread flour, turn out the dough, pre-shape into a loose round, and rest 20 minutes.
9. Dust a banneton or towel-lined bowl with the rest of the reserved bread flour. Shape the dough into a tight boule, brush the top lightly with water, roll the top in the oat-sesame mixture, and place it seam side up in the banneton.
10. Cover and cold-proof in the fridge for 12 to 16 hours, until it springs back slowly when poked.
11. Place a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
12. Turn the cold dough onto parchment, seed side up, and score a deep cross. Lower it into the hot Dutch oven, cover, and bake 20 minutes.
13. Uncover, reduce to 450°F (230°C), and bake 20 to 25 minutes more, until deep brown and crisp and the center reads 205°F (96°C).
14. Cool the loaf on a rack for at least 2 hours before slicing into 12 slices.