Walnut Thyme Cheddar Rye Sourdough Batard

Steps

1. Starter schedule: about 5 hours before mixing, give your starter its usual 1:1:1 feeding by weight and keep it at about 75°F (24°C); it peaks in 4 to 6 hours, when doubled, domed and bubbly. Measure the sourdough starter for this loaf 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. Cube the cheddar and refrigerate it until needed. Soften the butter and set aside about one-sixth of it for brushing the baked loaf. Set aside about 10 g of the rye flour for dusting.
3. In a large bowl, whisk the lukewarm milk, lukewarm water, molasses and sourdough starter until the starter is dissolved.
4. Add the remaining rye flour and all the bread flour and mix until no dry patches remain. Cover and rest 30 minutes.
5. Sprinkle the salt over the dough and add the larger portion (five-sixths) of the softened butter; squeeze and fold with wet hands until fully absorbed. The dough is about 75% hydration (counting the water, the starter's water and the milk's water) and 2% salt, and it will feel sticky and pasty, which is normal for rye.
6. Bulk rise covered at about 75°F (24°C) for 4 to 5 hours. During the first 90 minutes, do 3 sets of stretch-and-folds 30 minutes apart with wet hands; on the first set, fold in the walnuts, cheddar and thyme until evenly spread.
7. Bulk is done when the dough has grown by about half, looks puffy and shows small bubbles on the surface and sides.
8. Dust the counter with half of the reserved rye flour, turn the dough out, pat it into a rectangle, roll it up tightly into a batard and pinch the seam. Dust a banneton or towel-lined bowl with the rest of the reserved rye flour and place the loaf in it seam side up.
9. Proof covered at about 75°F (24°C) for 1 hour, then refrigerate overnight, 12 to 14 hours.
10. Preheat the oven to 425°F (220°C) with a rack in the middle. Turn the cold loaf onto a parchment-lined baking sheet and make one shallow slash down its length.
11. Bake 20 minutes, then lower the oven to 375°F (190°C) and bake 25 to 30 minutes more, until deep brown and the center reads 190°F (88°C); tent with foil if the cheese browns too fast.
12. Right out of the oven, brush the loaf with the reserved butter, then cover it loosely with a clean towel to keep the crust soft.
13. Cool on a rack at least 2 hours before slicing into 12 slices; rye needs this time to set its crumb.