In a large bowl, whisk flour, fine salt and yeast.

Pour in the lukewarm water and stir with a fork, or spatula, until all the flour is incorporated. You should have a loose ball of focaccia dough.

Scrape down the sides of the bowl to tidy, and drizzle the top and sides of the focaccia dough with 2 tablespoons olive oil, spreading it under and over the top of the dough.

Cover the bowl, and let this rise for 1 ½ -2 hours on the counter (until doubled), or for 24-72 hours in the refrigerator (for the best flavor and airy texture).

Pour 2-3 tablespoons olive oil on the bottom and sides of the 9×13-inch baking dish (see notes for using glass and ceramic), 10×14-inch Detroit-style pan (in my photos).

With an oiled hand loosen the edges of the dough from the bowl, and do a set of “stretch and folds”; use your fingers to pull the dough at the edge of the bowl, up and over and across itself, then turn the bowl 90 degrees, and repeat this 6 times, until you have a ball.

Pour the focaccia dough ball into the generously oiled pan. (I used a 10×14-inch pan) Let the dough rise uncovered and stretch out over the pan until doubled, roughly 45 minutes. Or allow 2-4 hours at room temperature for the best airy texture and flavor.

Preheat the oven to 425F (or 400F convection)

Drizzle the last tablespoon of olive oil over the dough, and with oiled fingers, poke holes straight down into the dough, creating deep dimples, gently nudging the dough towards the edges. If the dough resists, let it rest for 5 minutes, and resume. Sprinkle with the flaky sea salt and rosemary.

Bake on the middle rack for 25-30 minutes, until puffed, golden brown, and the bottom is crisp and golden. Let rest 10 minutes before slicing.