Soft Parmesan Basil Focaccia-Style Sourdough Boule

Steps

1. Day 1, 8 a.m.: Feed the sourdough starter with equal weights of flour and water from your usual stock and leave it at about 75°F (24°C). It should peak in 4 to 6 hours, doubled, domed and bubbly; measure out the sourdough starter for this loaf at its peak.
2. Around 1 p.m.: In a large bowl, stir the warm whole milk, the water and the all-purpose flour until no dry flour remains. Cover and rest 30 minutes.
3. Add the peak sourdough starter and the salt to the dough and squeeze and fold with wet hands for 3 to 4 minutes until evenly mixed. Counting the starter and the water in the milk, the dough is about 73% hydration and 1.5% salt, with the Parmesan adding more savory saltiness.
4. Drizzle in two-thirds of the olive oil and squeeze until the dough absorbs it and turns glossy.
5. Bulk rise, covered, at about 75°F (24°C) for 4 to 5 hours. Do 4 sets of stretch-and-folds 30 minutes apart in the first 2 hours. On the second set, scatter the basil and three-quarters of the Parmesan over the dough and fold them in. The dough is ready when it has grown about 50%, feels airy and jiggles.
6. Turn the dough onto the counter, pre-shape into a loose round and rest 20 minutes, then shape a tight boule by pulling it toward you to build surface tension.
7. Place the boule seam side up in a floured bowl or banneton, cover and proof in the fridge overnight, 12 to 14 hours.
8. Day 2: Line a baking sheet with parchment and preheat the oven to 375°F (190°C) for 30 minutes.
9. Turn the cold boule onto the parchment. Brush the top with half of the remaining olive oil, press fingertips into it to make shallow focaccia-style dimples, and sprinkle on the remaining Parmesan. Rest 20 minutes while the oven finishes heating.
10. Bake uncovered for 35 to 40 minutes, until golden and 190°F (88°C) in the center; tent loosely with foil if the cheese browns too fast.
11. Right out of the oven, brush the loaf with the last of the olive oil to keep the crust soft.
12. Cool the loaf on a rack for at least 2 hours before cutting it into 12 slices.