Sourdough Garlic Spinach Flatbreads with Lemon

Steps

1. Day 1, morning: feed your sourdough starter on its usual schedule and leave it at about 75°F (24°C) for 4 to 6 hours, until doubled, domed and bubbly; measure out the sourdough-starter for this recipe at its peak.
2. In a large bowl, whisk the sourdough-starter into the lukewarm water until milky, then add the bread flour and whole wheat flour and mix until no dry patches remain. Cover and rest 30 minutes.
3. Sprinkle the salt and the first portion of olive oil (15 g) over the dough and squeeze and fold them in until smooth. The dough is about 71% hydration and 2% salt, counting the water and the bread flour and whole wheat flour, plus what the starter holds.
4. 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, then leave it alone until it has grown about 50%, looks domed and jiggles with bubbles at the edges.
5. Turn the dough onto a clean counter, divide it into 2 equal pieces and shape each into a tight ball. Place them in separate lidded containers and cold proof in the fridge for 12 to 16 hours overnight.
6. Day 2: take the dough balls out and let them warm on the counter at about 75°F (24°C) for 1 to 1½ hours, until soft, puffy and springing back slowly when poked.
7. Meanwhile, place a baking steel, stone or upturned sheet pan on the lowest rack and preheat the oven to 500°F (260°C) for at least 45 minutes.
8. Make the garlic oil: warm the second portion of olive oil (30 g) with the garlic in a small skillet over low heat for 3 to 4 minutes, just until the garlic is soft and pale gold. Remove from the heat, add the spinach and toss until barely wilted, then stir in the red pepper flakes.
9. Dust a sheet of parchment with half of the cornmeal. Stretch one dough ball by hand into a rough 12-inch oval flatbread on it, leaving a slightly thicker rim.
10. Spread half of the garlic spinach over the dough, then scatter half of the mozzarella and half of the Parmesan on top.
11. Slide the parchment onto the hot steel and bake 9 to 12 minutes, until the crust is deep golden and blistered, the bottom is crisp and the cheese is bubbling; the crust should read about 200°F (93°C) inside.
12. While the first pizza bakes, shape the second dough ball on parchment dusted with the remaining half of the cornmeal and top it with the remaining half of the garlic spinach, mozzarella and Parmesan; bake it the same way.
13. Move each pizza to a rack, scatter half of the lemon zest over each, cool 3 minutes, then cut each pizza into 6 slices.