Oat Porridge Rosemary Spelt Sourdough Boule

Steps

1. Evening before, about 9 pm: feed your sourdough starter from your usual starter supplies (not from this recipe's ingredients) and leave it at about 75°F (24°C); it should double and peak in 4 to 8 hours, domed and bubbly.
2. Same evening: make the soaker. Stir 80 g of the oats, the flaxseed and 120 g of the water in a bowl, cover and leave at room temperature overnight so the oats turn soft and porridge-like.
3. Morning: toast the pumpkin seeds and sesame seeds in a dry skillet over medium heat for 3 to 4 minutes until fragrant, then cool them.
4. When the starter peaks, mix the spelt flour, bread flour, honey and the remaining 350 g of water in a large bowl until no dry patches remain. Cover and rest 45 minutes. The dough water gives about 70% hydration and the salt is 2%; the soaker adds extra moisture on top.
5. Add the sourdough starter and salt, squeezing and folding with wet hands for 3 to 4 minutes until combined.
6. Add the oat soaker, the toasted pumpkin seeds and sesame seeds, and the rosemary, folding until evenly spread through the dough.
7. Bulk rise covered at about 75°F (24°C) for 3.5 to 4.5 hours. During the first 1.5 hours do 3 gentle sets of stretch-and-folds, 30 minutes apart; spelt is delicate, so stop once the dough feels smooth. Bulk is done when it has risen about 50%, feels airy and shows bubbles at the sides.
8. Turn the dough onto a lightly dampened counter, pre-shape into a loose round with wet hands and rest 20 minutes.
9. Shape into a tight boule. Mist the top with water and roll it in the 20 g of oats reserved for the topping, then set it oat-side down in a towel-lined bowl or banneton; the oat coating keeps it from sticking.
10. Cover and cold proof in the fridge for 10 to 14 hours overnight.
11. Next morning, set a lidded Dutch oven in the oven and preheat to 475°F (245°C) for 45 minutes.
12. Turn the cold dough onto parchment, score it with one confident slash and lower it into the hot Dutch oven.
13. Bake covered for 20 minutes, then uncover, reduce to 450°F (230°C) and bake 22 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; this sets the crumb and keeps the crust crackly.