01 -
Whisk the water, starter, sugar, and vanilla in a large bowl. Add the bread flour and cocoa powder and mix until no dry spots remain. Cover and rest for 30 minutes.
02 -
Sprinkle the salt over the dough and add 35 g olive oil. Squeeze and fold the dough until the oil is mostly absorbed and the dough feels smoother.
03 -
Do 3 sets of stretch and folds over 90 minutes, covering the bowl between sets. Let the dough rise at room temperature until puffy and increased by about 60 percent, 4-6 hours.
04 -
Coat a 9x13-inch metal pan with 2 tablespoons olive oil. Transfer the dough to the pan, turn it to coat, and gently stretch it toward the corners.
05 -
Cover the pan and let the dough proof until airy, bubbly, and jiggly when the pan is gently shaken, about 2-3 hours.
06 -
Heat the oven to 425°F. Drizzle the remaining 1 tablespoon olive oil over the dough, oil your fingertips, and press deep dimples all over. Scatter chocolate chips, flaky salt, and optional coarse sugar on top.
07 -
Bake for 24-28 minutes, until the edges are set and the center springs back lightly. Cool in the pan for 10 minutes, then move to a rack and cool at least 30 minutes before slicing.