Toasted Oat Porridge Seeded Sourdough Batard

Steps

1. Morning, about 8 am: feed your starter with equal weights of flour and water and leave it at about 75°F (24°C); it should double and peak, bubbly and domed, in 4 to 6 hours.
2. While the starter rises, make the oat porridge soaker: toast 70 g of the oats (keep the other 10 g for the crust) with the pumpkin seeds and sesame seeds in a dry skillet over medium heat, stirring, for 4 to 5 minutes until golden and nutty.
3. Tip the toasted oats and seeds into a bowl, stir in the flaxseed, and pour over the 100 g of boiling water. Cover and cool to room temperature; the oats will absorb the water into a thick porridge.
4. When the starter peaks, stir it into the remaining 320 g of lukewarm water with the maple syrup in a large bowl until milky.
5. Add the flour and mix until no dry bits remain. Cover and rest 30 minutes.
6. Sprinkle the salt over the dough, squeeze it in, and knead in the bowl for 2 to 3 minutes. The dough is about 71% hydration (plus the soaker's water) and about 2.2% salt.
7. Bulk rise at about 75°F (24°C) for 4 to 5 hours. Every 30 minutes for the first 2 hours, do a set of stretch-and-folds; on the second set, spread the oat-seed soaker over the dough and fold it in until evenly distributed.
8. Bulk is done when the dough has grown by about 50 to 75%, feels airy and jiggly, and shows bubbles on the sides and top.
9. Turn the dough onto a lightly floured counter, pre-shape into a loose round, and rest 20 minutes. Shape into a long, tight batard so the slices come out even for sandwiches.
10. Mist or wet the top of the loaf and roll it in the reserved 10 g of oats, then place it seam side up in a floured banneton or towel-lined bowl.
11. Cover and cold proof in the fridge for 12 to 14 hours overnight.
12. Next day, place a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
13. Turn the cold loaf onto parchment, score one long slash down its length, and lower it into the hot Dutch oven. Cover and bake 20 minutes.
14. Uncover, lower the oven to 450°F (230°C), and bake 25 to 30 minutes more, until the crust is a deep mahogany brown and the center reads 205 to 210°F (96 to 99°C).
15. Cool the loaf on a rack for at least 2 hours before cutting into 12 slices.