Make the dough: 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. Cover the bowl with a cloth bowl cover, tea towel, or plastic wrap and place in the refrigerator immediately for at least 12 hours.

Line two 8- or 9-inch pie plates (see notes above for other options) with parchment paper or grease with butter or coat with nonstick cooking spray. Pour a tablespoon of oil into the center of each pan. Using two forks, deflate the dough by releasing it from the sides of the bowl and pulling it toward the center.

Rotate the bowl in quarter turns as you deflate, turning the mass into a rough ball. Use the forks to split the dough into two equal pieces. Place one piece into one of the prepared pans. Roll the dough ball in the oil to coat it all over, forming a rough ball. Repeat with the remaining piece. Let the dough balls rest for 2 to 4 hours depending on the temperature of your kitchen—when the dough has puffed considerably and is light to the touch, it’s ready.

Set a rack in the middle of the oven and preheat it to 425 degress. Pour another tablespoon of oil over each round of 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 all over with flaky sea salt.

Transfer the pans to the oven and bake for 25 to 30 minutes, until the underside is golden and crisp. Remove the pans from the oven and transfer the focaccia to cooling racks. Let it cool for 10 minutes before cutting and serving.