Sharp Cheddar Walnut Spelt Sourdough Boule

Steps

1. In the morning, give your starter its usual 1:1:1 feed (equal weights of starter, fresh feed and water) and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, domed and bubbly and a spoonful floats in water.
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. Cube the cheddar and keep it in the fridge.
3. When the starter is near its peak, mix the whole spelt flour, 100 g of the bread flour (set the remaining 10 g aside for dusting) and 330 g of the water (all but 20 g) in a large bowl until no dry patches remain. Cover and rest 45 minutes (autolyse).
4. Add the starter to the dough and pinch and fold it in for 2 to 3 minutes. Sprinkle the salt over the dough with the remaining 20 g of water and squeeze it through until absorbed. The dough is about 70% hydration and 1.8% salt.
5. Start the bulk rise at about 75°F (24°C). After 30 minutes, do the first set of stretch-and-folds: lift each side of the dough and fold it over the center, turning the bowl four times.
6. After another 30 minutes, stretch the dough into a thin rectangle on a damp counter, scatter the walnuts, cheddar and black pepper evenly over it, then fold it into thirds both ways and return it to the bowl.
7. Do two more sets of stretch-and-folds 30 minutes apart, being gentle so the cheese stays in pieces. Then leave the dough covered until it has risen about 50%, looks domed and jiggly with bubbles at the edges, about 4 to 5 hours of bulk in total from adding the starter. Spelt ferments quickly, so watch the dough more than the clock.
8. Dust the counter with half of the reserved bread flour, turn the dough out, pre-shape into a loose round and rest 20 minutes. Dust a banneton or towel-lined bowl with the other half of the reserved bread flour. Shape into a tight boule, tucking any exposed cheese underneath, and place it seam side up in the banneton.
9. Proof at room temperature for 1 hour, then cover and cold proof in the fridge for 12 to 14 hours.
10. Place a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes to 1 hour.
11. Turn the cold dough onto parchment, score a deep cross across the top, and lower it into the hot Dutch oven. Cover, reduce the oven to 460°F (238°C) and bake 20 minutes.
12. Remove the lid and bake 25 to 30 minutes more, until the crust is a deep mahogany brown and the center reads 205°F (96°C). Some cheese may bubble and crisp on the crust.
13. Cool the loaf on a rack for at least 2 hours before slicing into 12 slices, so the crumb and melted cheese set.