Maple Oat Porridge Seeded Whole Wheat Batard

Steps

1. Day 1, morning: feed your sourdough starter on its usual schedule and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, domed and bubbly; that is its peak.
2. While the starter rises, make the oat porridge: pour the boiling portion of the water (130 g) over the porridge portion of the oats (80 g), stir, cover and cool to lukewarm, about 1 hour. Stir the ground flaxseed into the porridge so it soaks too.
3. When the starter peaks, whisk the sourdough starter with the lukewarm portion of the water (200 g), the dough portion of the whole milk (70 g) and the maple syrup in a large bowl.
4. Add the whole wheat flour and the bread flour and mix until no dry patches remain. Cover and rest 45 minutes so the bran softens.
5. Add the salt and the softened dough portion of the butter (25 g) and squeeze them through the dough until fully absorbed, about 3 minutes. The dough is about 70% hydration (water plus the starter's water, before the milk and porridge) and 2% salt.
6. Add the oat porridge, the pumpkin seeds and the sesame seeds and fold until evenly spread; the dough will be sticky.
7. 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, with wet hands. Bulk is done when the dough has grown about 50%, feels airy and jiggles.
8. Turn the dough onto a lightly wet counter, pre-shape into a loose round and rest 20 minutes. Shape into a tight batard, roll the top across a damp towel, then press it into the topping portion of the oats (10 g).
9. Place seam side up in a towel-lined banneton or loaf-shaped bowl, cover and cold proof in the fridge 12 to 14 hours overnight.
10. Day 2: line a sheet pan with parchment and preheat the oven to 400°F (204°C) for 30 minutes, with a rack in the middle.
11. Turn the batard onto the parchment oat side up, brush gently with the brushing portion of the whole milk (10 g) and make one shallow slash along its length.
12. Bake 40 to 45 minutes, until deep golden and the center reads 190°F (88°C), since the dough is enriched with milk and butter.
13. Brush the hot crust with the melted brushing portion of the butter (5 g), then cool on a rack loosely covered with a clean towel to keep the crust soft, at least 2 hours, before slicing into 12 slices.