In a large bowl, whisk together the flour, salt, and instant yeast.
Add the water and mix with a spatula or wooden spoon until the dough comes together in a sticky, shaggy ball.
Cover the bowl and let it rest for 30 minutes to allow the flour to hydrate.
After the initial rest, perform 1 gentle round of stretch-and-fold: lightly wet your hand, grab an edge of the dough, stretch it upward, and fold it over the center.
Rotate the bowl and repeat until all edges have been folded in. This step is optional but helps develop gluten for a light, airy texture.
Lightly grease a large bowl with 1 tablespoon of olive oil and coat the dough.
Cover tightly and refrigerate for 12–24 hours. The long, cold proof develops flavor and encourages an open crumb.
When ready to bake, generously butter a 9×13-inch pan (or similar) and drizzle with 1–2 tablespoons olive oil.
Transfer the dough into the pan, gently pressing it out to fit. Let it rest at room temperature for 1–2 hours until noticeably puffy.
Preheat the oven to 425°F.
Use oiled fingertips to create deep dimples in the dough.
Drizzle 1–2 tablespoons of olive oil over the top, sprinkle with rosemary (if using) and flaky salt. Press the toppings slightly into the dough.
Bake for 25–30 minutes, until golden brown on top and crisp on the bottom.
Remove from the pan and cool on a wire rack for 10 minutes before slicing.