In a large bowl, whisk together the flour, salt, and instant yeast. Add the water. Using a rubber spatula, mix until the liquid is absorbed and the ingredients form a sticky dough ball. Rub the surface of the dough lightly with olive oil.

Let rise on counter for 15 minutes, and then scoop and fold in sides over itself. Do this again after 15 more minutes and then cover the bowl with a lid and place in the refrigerator immediately for 12-48 hours.

Line two 8- or 9-inch pie plates or a 9×13-inch pan (see notes above) with parchment paper or grease with butter or coat with nonstick cooking spray.

Pull dough out of oven for 30 minutes before handling.

Grease a 9×13-inch pan. Deflate the dough by releasing it from the sides of the bowl and pulling it toward the center. Place and lightly stretch the dough into the pan. Let the dough rest for 3 to 4 hours depending on the temperature of your kitchen.

Set a rack in the middle of the oven and preheat it to 425°F. Pour a tablespoon of oil over dough. Rub your hands lightly in the oil to coat, then, using all of your fingers, press straight down to create deep dimples. If necessary, gently stretch the dough as you dimple to allow the dough to fill the pan. Sprinkle with flaky sea salt all over.

Transfer the pans or pan to the oven and bake for 25 to 30 minutes, until the underside is golden and crisp. Remove the pans or pan from the oven and transfer the focaccia to a cooling rack. Let it cool for 10 minutes before cutting and serving; let it cool completely if you are halving it with the intention of making a sandwich.

When it has completely cooled, transfer it to an airtight bag or vessel and store it at room temperature for up to 3 days. Otherwise, freeze it for up to 3 months. Always reheat it on subsequent days to revive its crust: 350ºF for 15 minutes.