Cheddar Walnut Rosemary Seeded Sourdough Boule

Steps

1. Day 1, morning: feed your sourdough starter as you usually do, with equal weights of its regular feed and water (that feed is separate from this recipe's ingredients), and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, domed and bubbly. You'll use the sourdough starter at its peak.
2. While the starter rises, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, cool, and chop roughly. Cube the cheddar and keep it chilled.
3. When the starter peaks, stir together the all-purpose flour, the whole wheat flour and 320 g of the water until no dry patches remain. Cover and rest 45 minutes (autolyse).
4. Add the sourdough starter to the dough and squeeze it in with wet hands until even, about 3 minutes.
5. Sprinkle the salt over the dough, add the remaining 30 g of water, and squeeze and fold until the water is absorbed and the dough feels cohesive. This is about 73% hydration counting the starter, and about 2% salt.
6. Bulk rise at about 75°F (24°C) for 4 to 5 hours. After 30 minutes, do the first stretch-and-fold: spread the dough, scatter half the cheddar, half the walnuts, all the rosemary and all the black pepper, then fold the dough over itself from all four sides. After another 30 minutes, add the remaining half of the cheddar and the remaining half of the walnuts with a second set of folds. Do two more sets of stretch-and-folds 30 minutes apart, then leave the dough undisturbed.
7. Bulk is done when the dough has grown about 50%, looks domed and airy with bubbles on the sides, and jiggles when the bowl is shaken.
8. Tip the dough onto a clean, dry counter, pre-shape it into a loose round, and rest it uncovered 20 minutes.
9. Mix the pumpkin seeds and sesame seeds on a plate. Shape the dough into a tight boule, wet the top lightly, roll the top in the seed mixture, and place it seed side down (seam side up) in a banneton or towel-lined bowl; the seeds keep it from sticking.
10. Cover and cold proof in the fridge for 12 to 16 hours overnight.
11. Day 2: place a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes.
12. Turn the cold dough onto parchment seed side up, score one deep slash, and lower it into the hot Dutch oven. Cover, reduce the oven to 450°F (230°C) and bake 20 minutes.
13. Remove the lid and bake 22 to 25 minutes more, until deep golden brown and crisp and the center reads 205 to 210°F (96 to 99°C).
14. Cool the loaf on a rack at least 2 hours before slicing into 12 slices so the crumb sets and the crust stays crisp.