Dill Garlic Cheddar Sourdough Sandwich Batard

Steps

1. Feed the sourdough starter about 4 to 6 hours before mixing, using your usual feeding of equal weights of starter food and water (this feeding is separate from the recipe amounts). Leave it at about 75°F (24°C) until doubled, domed and bubbly; it is ready when a small spoonful floats in water.
2. While the starter rises, prepare the add-ins: cube the cheddar, finely chop the dill and mince the garlic. Toss the dill and garlic together in a small bowl and keep the cheddar chilled.
3. Autolyse: in a large bowl, mix the bread flour and the whole wheat flour with 320 g of the water (all but 30 g) until no dry bits remain. Cover and rest 45 minutes.
4. Add the peaked sourdough starter and squeeze it through the dough with wet hands for 2 to 3 minutes. Rest 20 minutes.
5. Sprinkle the salt over the dough, drizzle with half of the olive oil and the remaining 30 g of water, and squeeze and fold until fully absorbed and the dough feels smooth, about 3 minutes. This dough is about 70% hydration (75% counting the starter's water) and 2% salt.
6. Bulk rise at about 75°F (24°C) for 4 1/2 to 5 1/2 hours. After the first 30 minutes, stretch the dough thin on a wet counter, scatter the dill-garlic mixture and the cheddar evenly over it, fold it back into a ball and return it to the bowl.
7. Do 3 more sets of stretch-and-folds, 30 minutes apart, then leave the dough covered until it has grown by about 50%, looks domed and jiggly, and shows bubbles on the sides.
8. Preshape: rub the remaining half of the olive oil on a clean counter, turn the dough onto it, round it loosely and rest it uncovered 20 to 30 minutes.
9. Shape a tight batard, tucking any exposed cheese underneath, and set it seam-side up in an oval bowl lined with parchment.
10. Cover and cold proof in the fridge for 12 to 16 hours, until the dough springs back slowly when poked.
11. Place a Dutch oven with its lid in the oven and preheat to 500°F (260°C) for 45 minutes.
12. Lift the cold batard out on its parchment, turn it seam-side down, score one long, deep slash down its length, and lower it into the hot Dutch oven. Cover, reduce the oven to 475°F (245°C) and bake 20 minutes.
13. Uncover, reduce 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°F (96°C).
14. Cool the loaf on a rack for at least 2 hours before cutting into 12 slices, so the crumb sets and slices cleanly for sandwiches.