Toasted Walnut Country Sourdough Boule

Steps

1. Night before baking day, around 9 pm: feed your starter with your usual feeding mix of equal weights of grain and water, making a little more than the sourdough starter amount you need, and keep it at about 75°F (24°C). It should peak, doubled and domed with bubbles, in 8 to 12 hours, by morning.
2. Morning, 9 am: preheat the oven to 350°F (175°C). Toast the walnuts on a baking sheet for 8 to 10 minutes until fragrant, cool completely, then chop roughly.
3. In a large bowl, mix the bread flour, the whole wheat flour and 340 g of the water (all but 20 g) until no dry patches remain. Cover and rest 45 minutes (autolyse).
4. Add the sourdough starter and squeeze it through the dough. Rest 15 minutes, then sprinkle on the salt and the remaining 20 g of water and pinch and fold until absorbed. This is about 72% hydration and 2% salt, counting the bread flour and whole wheat flour with the added water.
5. 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; at the second set, spread the dough out, scatter the toasted walnuts over it and fold them in.
6. Bulk is done when the dough has grown about 50%, feels airy and jiggly, and shows bubbles on the sides and top.
7. Turn the dough onto a clean, dry counter, pre-shape into a loose round and rest 20 minutes uncovered. Dust a banneton or towel-lined bowl with half of the cornmeal. Shape a tight boule and place it seam side up in the banneton.
8. Cover and cold proof in the fridge overnight, 12 to 16 hours, until the dough springs back slowly when poked.
9. Next morning: put a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes.
10. Dust a piece of parchment with the remaining half of the cornmeal, turn the cold dough out onto it and score a deep slash or a cross with a sharp blade.
11. Lower the loaf on its parchment into the hot Dutch oven, cover and bake 20 minutes. Reduce to 450°F (230°C), uncover and bake 25 to 30 minutes more until the crust is deep mahogany and the center reads 205–210°F (96–99°C).
12. Cool the boule on a rack for at least 2 hours before slicing into 12 slices.