Maple Oat Porridge Seeded Country Boule

Steps

1. The morning before baking (about 9 a.m.), refresh your sourdough starter with its usual 1:1:1 feeding from your own supply and leave it at about 75°F (24°C); it should peak, doubled and bubbly, in 4 to 6 hours.
2. While the starter rises, make the porridge: in a small pot, simmer 70 g of the oats with the whole milk over medium-low heat for 4 to 5 minutes, stirring, until thick. Stir in the maple syrup and 15 g of the butter, then cool to room temperature, about 1 hour.
3. In a large bowl, mix the all-purpose flour and the whole-wheat flour with 230 g of the water until no dry patches remain. Cover and rest 45 minutes (autolyse).
4. Add the peaked sourdough starter and squeeze it into the dough. Add the salt and pinch and fold until combined, about 3 minutes.
5. Add the cooled oat porridge, 15 g of the sesame seeds, the flaxseed and the pumpkin seeds; squeeze and fold until evenly spread, about 4 minutes. The dough is about 48% hydration from the water alone, close to 80% counting the milk and starter, with 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 it alone until about 50% larger, domed and jiggly with bubbles on the sides.
7. Turn the dough onto a lightly dampened counter, pre-shape into a loose round and rest 20 minutes. Shape into a tight boule.
8. Mix the remaining 10 g of sesame seeds with the remaining 10 g of oats on a plate. Brush the top of the boule with the remaining 20 g of water and roll it in the seed-oat mix.
9. Place seam-side up in a towel-lined bowl, cover and proof in the fridge overnight, 12 to 14 hours.
10. The next morning, put a Dutch oven with its lid in the oven and preheat to 450°F (230°C) for 45 minutes.
11. Turn the cold boule onto parchment, score the top, and lower it into the hot Dutch oven. Bake covered 20 minutes, then lower to 425°F (220°C) and bake uncovered 18 to 22 minutes, until golden and 205°F (96°C) in the center.
12. Brush the hot crust with the remaining 5 g of melted butter to keep it soft, and cover loosely with a clean towel.
13. Cool on a rack at least 2 hours before slicing into 12 slices.