Sharp Cheddar Mustard Pepper Rye Batard

Steps

1. Day 1, about 8 a.m.: feed your sourdough starter with its usual feed and an equal weight of water, and leave it at about 75°F (24°C). It should peak, doubled and domed with lots of bubbles, in 4 to 6 hours. Use the sourdough-starter at its peak.
2. Meanwhile, prepare the add-ins: cut the cheddar into cubes and keep it in the fridge, slice the green onion and crack the black pepper. Set aside about 10 g of the bread flour for dusting later; the rest (about 170 g) goes into the dough.
3. When the starter peaks (about 1 p.m.), whisk the water, the sourdough-starter and the mustard in a large bowl until the starter is dissolved.
4. Add the rye flour, the dough portion of the bread flour and the salt, and mix with a wet hand or stiff spatula until no dry patches remain. The dough will be sticky and paste-like; that is normal for rye. Counting the starter, this is about 80% hydration and 1.8% salt.
5. Cover and rest 30 minutes at about 75°F (24°C).
6. Scatter the cheddar, the black pepper and the green onion over the dough and fold them in with wet hands until evenly spread.
7. Bulk rise, covered, at about 75°F (24°C) for 3 1/2 to 4 hours. During the first 1 1/2 hours do 3 sets of gentle stretch-and-folds with wet hands, 30 minutes apart, then leave it alone. It is ready when it has grown by about half, looks puffy, and shows small bubbles and cracks on the surface.
8. Dust a work surface and a banneton or towel-lined oval bowl with half of the reserved bread flour. Turn out the dough and, with hands dusted in the remaining half of the reserved bread flour, gently pat and roll it into a tight oval batard, pinching the seam closed. Place it seam side up in the banneton.
9. Cover and cold proof in the fridge overnight, 12 to 14 hours. It is ready when it has risen slightly and springs back slowly when lightly poked.
10. Day 2: put a Dutch oven with its lid in the oven and preheat to 475°F (245°C) for 45 minutes.
11. Turn the cold dough onto parchment, score one long slash down the top, and lower it into the hot Dutch oven. Bake covered for 20 minutes.
12. Uncover, lower the heat to 450°F (230°C) and bake 25 to 30 minutes more, until the crust is deep brown and crisp and the center reads 205–210°F (96–99°C). Melted cheese spots on the crust are a bonus.
13. Cool the loaf on a rack for at least 3 hours before slicing, since rye crumb keeps setting as it cools. Cut into 12 slices.