Soft Spelt Feta, Walnut and Oregano Batard

Steps

1. About 5 hours before mixing, feed the sourdough starter with its usual feed at a 1:1:1 ratio by weight and keep it at about 75°F (24°C); it is ready when doubled, domed and bubbly, usually 4 to 6 hours.
2. While the starter rises, toast the walnuts in a dry skillet over medium heat for 4 to 5 minutes until fragrant, cool, then chop. Crumble the feta and pat it dry on a paper towel.
3. In a large bowl, stir the water, milk, honey and olive oil together. Add the peaked sourdough starter and whisk until milky.
4. Add the spelt flour and bread flour and mix by hand until no dry patches remain. Cover and rest 30 minutes.
5. Sprinkle the salt and oregano over the dough and squeeze them in with wet hands for 2 minutes until evenly mixed. This dough is about 70% hydration (counting the water in the milk and starter) and about 1.5% salt, kept low because the feta is salty.
6. Begin the bulk rise at about 75°F (24°C), covered, for about 4 hours. After 30 minutes, do the first set of stretch-and-folds: spread the walnuts and feta over the dough, then lift and fold each side over the center four times to work them in.
7. Do two more sets of stretch-and-folds 30 minutes apart, then leave the dough undisturbed; it is ready when it has grown about 50%, feels airy and jiggles at the edges. Spelt is delicate, so handle it gently and don't let it overproof.
8. Mist the counter lightly with water, turn out the dough, pre-shape into a loose round with wet hands and rest 20 minutes uncovered.
9. Shape into a snug batard by folding the sides to the middle, then rolling it up tightly from the top and pinching the seam. Set it seam-side down on a sheet of parchment inside an oval basket or loaf-shaped bowl.
10. Cover and cold proof in the fridge overnight, 10 to 14 hours.
11. Preheat the oven to 400°F (200°C) with a rack in the middle.
12. Lift the dough by its parchment onto a baking sheet and make one shallow slash along the length.
13. Bake uncovered, without steam, for 35 to 40 minutes until deep golden and the center reaches 190°F (88°C) on a thermometer; tent with foil after 25 minutes if the feta on top browns fast.
14. Brush the hot loaf all over with the melted butter, then cover it loosely with a clean kitchen towel to keep the crust soft.
15. Cool on a rack for at least 2 hours before slicing into 12 slices for sandwiches.