3-Day Cold-Fermented Focaccia

Ingredients

• 500 g bread flour (4 cups)
• 390 g lukewarm water (1 2/3 cups), about 78% hydration
• 10 g fine sea salt (1 3/4 tsp)
• 2 g instant yeast (a scant 3/4 tsp)
• 20 g olive oil for the dough (1 1/2 tbsp)
• 45 g olive oil for the pan and the top (3 tbsp)
• 1 tsp flaky salt, for the top
• 1 tbsp fresh rosemary leaves (or 1 tsp dried)
• Optional toppings: a handful of cherry tomatoes, halved; pitted olives; a few thin slices of garlic

Steps

1. The plan: Day 1 (evening, about 20 minutes of hands-on time): mix and fold, then into the fridge. Day 2: nothing to do. Day 3: pan it in the morning, proof 2 to 4 hours at room temperature, bake 25 minutes. About 30 minutes of actual work in total.
2. Day 1, mix: In a large bowl, stir the yeast into the water until it disappears. Add the flour and salt and mix with a spoon or a wet hand until no dry flour is left. It will be a shaggy, sticky dough. Cover and rest 30 minutes.
3. Day 1, oil: Pour the 20 g olive oil over the dough and squeeze and pinch it in with a wet hand until it is absorbed, about a minute.
4. Day 1, stretch and folds: With a wet hand, grab one edge of the dough, stretch it up and fold it over the middle. Turn the bowl a quarter turn and repeat four times. Cover. Do this 3 or 4 times, 30 minutes apart. The dough goes from shaggy to smooth and bouncy.
5. Day 1, into the fridge: After the last fold, cover the bowl tightly (a lid or plastic wrap) and put it in the fridge for the night.
6. Day 2, leave it alone: The dough stays in the fridge and slowly bubbles and rises a little. Optional: one more set of folds if you walk past it, then straight back in.
7. Day 3, pan: Pour 2 tbsp of the olive oil into a 9x13 inch (23x33 cm) pan, or a half-sheet pan for a thinner, crispier focaccia. Tip the cold dough in, fold it once onto itself, flip it seam side down and turn it to coat in oil. Cover loosely.
8. Day 3, proof: Let it sit at room temperature 2 to 4 hours, until the dough has spread to fill the pan and looks puffy and full of bubbles. A cold kitchen takes the longer end.
9. Day 3, heat: 30 minutes before baking, heat the oven to 230°C / 450°F with the rack in the middle.
10. Day 3, dimple: Drizzle the last 1 tbsp olive oil over the top. Oil your fingertips and press straight down all over the dough, right to the bottom of the pan. Scatter the flaky salt and rosemary, and press in the tomatoes, olives or garlic if using.
11. Day 3, bake: 22 to 28 minutes, until the top is deep golden and the bottom is crisp (lift a corner with a spatula to check).
12. Rest 5 minutes, then slide it out of the pan onto a rack so the bottom stays crisp. Cut into squares. Best warm, and still great the next day, toasted.