Mix & first rise

1. In a large bowl, whisk the flour and instant yeast together.
2. Add the water and 2 tbsp / 30 ml of the olive oil. Stir with a sturdy spoon until no dry flour remains and you have a sticky, shaggy dough.
3. Sprinkle in the fine sea salt and stir again until it’s evenly distributed (the dough will look rough but cohesive).
4. Cover tightly and let rise at room temperature until very puffy and bubbly, 1.5–2.5 hours. It’s ready when the surface looks airy and it jiggles when you nudge the bowl.

Pan, rest, and dimple

1. Pour 2 tbsp / 30 ml olive oil into a 9×13-inch / 23×33 cm pan and spread it to coat the bottom and corners well.
2. Scrape the dough into the pan. Turn it once to lightly coat both sides in oil.
3. Let the dough rest 15 minutes, uncovered. If it tightens and resists stretching, that’s normal.
4. With oiled fingertips, gently stretch the dough toward the corners. If it springs back, rest 10 minutes, then stretch again until it mostly fills the pan.
5. Cover and let proof until thick, marshmallowy, and visibly expanded, 45–90 minutes. A gentle poke should leave an indentation that slowly springs back.
6. Heat the oven to 450°F / 230°C with a rack in the middle position.
7. Drizzle the remaining olive oil (about 2–4 tbsp / 30–60 ml) over the dough. Press your fingertips straight down to the pan to make deep dimples all over.
8. Sprinkle evenly with chopped rosemary and flaky salt.

Bake & finish

1. Bake at 450°F / 230°C for 20–25 minutes, rotating the pan once halfway through, until the top is deep golden brown and the edges look crisp and “fried” in oil.
2. Doneness cue: the focaccia should feel light for its size, the dimples should be bronzed, and the bottom should be well-browned when you lift a corner with a spatula.
3. Cool in the pan 10 minutes, then transfer to a rack. Slice warm or at room temperature.