Rosemary Garlic Cheddar Spelt Sourdough Boule

Steps

1. About 5 hours before mixing, feed your sourdough starter its usual equal-weight meal and leave it at about 75°F (24°C) for 4 to 6 hours, until it has doubled, is domed and bubbly, and a spoonful floats in water.
2. Prepare the garlic rosemary butter: melt the butter in a small pan over low heat, add the garlic and the rosemary, and cook gently for 2 minutes until fragrant but not browned. Pour half of this butter into a small bowl to cool for the dough; keep the remaining half in the pan for brushing the crust later.
3. In a large bowl, whisk the water, the milk and the peaked sourdough starter until the starter is loosened.
4. Add the spelt flour and the bread flour and mix by hand until no dry spelt flour or bread flour remains. Cover and rest for 45 minutes at about 75°F (24°C).
5. Sprinkle the salt and the cooled half of the garlic rosemary butter over the dough and squeeze and fold it in for 2 to 3 minutes until fully absorbed. The dough is about 62% hydration from water (counting the starter's water), with milk bringing the total liquid to about 70%, and 1.8% salt.
6. Begin the bulk rise, covered, at about 75°F (24°C). After 30 minutes, do the first set of stretch-and-folds: with wet hands, stretch one side up and fold it over, turning the bowl four times. Scatter one third of the cheddar over the dough during this set and fold it in.
7. Do three more sets of stretch-and-folds 30 minutes apart, adding the next third of the cheddar with the second set and the final third of the cheddar with the third set. Spelt dough is delicate, so fold gently.
8. Let the dough rest untouched for the rest of the bulk rise, about 2 1/2 to 3 more hours (5 hours total), until it has grown about 50%, looks puffy with bubbles at the edges and jiggles when the bowl is shaken.
9. Turn the dough onto a lightly dampened counter, pre-shape it into a loose round with wet hands and rest it 20 minutes. Shape into a tight boule, tucking any exposed cheddar underneath, and place it seam-side down on a sheet of parchment set inside a medium bowl.
10. Cover and proof in the fridge overnight, 12 to 14 hours, until slightly puffed; a wet fingertip poke should spring back slowly.
11. Place a Dutch oven with its lid in the oven and preheat to 425°F (220°C) for 45 minutes; the lower temperature keeps the crust soft.
12. Lift the cold dough by the parchment, score the top, lower it on the parchment into the hot Dutch oven, cover and bake 30 minutes. Uncover and bake 12 to 15 minutes more, until golden and the center reaches 190°F (88°C) on a thermometer.
13. Rewarm the remaining half of the garlic rosemary butter and brush it all over the hot loaf, then drape a clean towel over the bread to soften the crust as it cools.
14. Cool the boule on a rack for at least 2 hours before slicing into 12 slices.