Sourdough Focaccia

Verify the starter is active: it should float in water and smell pleasantly sour and yeasty. Combine warm water, starter, and olive oil in a large bowl. Add flour and salt. Mix with a wet hand or a spatula until no dry flour remains — about 3 minutes. Unlike commercial-yeast focaccia, this dough moves more slowly and benefits from patience. Cover and let rest 30 minutes for autolyse.

Perform four sets of coil folds over 2 hours: wet your hand, slide it under the dough, lift the whole mass, and let it fold under itself. Rotate the bowl 90 degrees and repeat. Perform one set every 30 minutes for the first two hours. After the fourth set, cover and let bulk ferment at room temperature until the dough is 50–75% larger, visibly bubbly, and airy — typically another 3–5 hours depending on room temperature and starter strength.

Pour a generous pool of olive oil (at least 3 tablespoons) into a half-sheet pan. Tip the dough in and gently stretch it toward the edges. Cover loosely with plastic and refrigerate overnight (8–12 hours) for a slow, cold final proof. The next day, remove from the refrigerator 2 hours before baking. The dough should have spread to fill most of the pan and look puffy and airy.

Drizzle additional olive oil generously over the surface of the dough. Spread your fingers wide and press them firmly through the dough to the pan bottom, creating deep dimples across the entire surface. Don't be timid — press firmly. Scatter fresh rosemary sprigs and flaky sea salt. The oil will pool in the dimples. Bake immediately at 230 C (450 F).

Bake at 230 C (450 F) on the lower-middle rack for 20–25 minutes until the top is deeply golden with darker blistered spots at the dimple peaks and the bottom is crispy and caramelized. Lift a corner with a spatula to check the bottom. Remove from the pan immediately to a wire rack to preserve the crisp bottom.