Step 1

In a large bowl, whisk together the flour, salt, and instant yeast

Step 2

Add the water

Step 3

Using a rubber spatula, mix until the liquid is absorbed and the ingredients form a sticky dough ball

Step 4

Rub the surface of the dough lightly with olive oil

Step 5

Cover the bowl with a damp tea towel, cloth bowl cover, or plastic wrap and place in the refrigerator immediately for at least 12 hours or for as long as three days

Step 6

Line 9×13-inch pan with parchment paper or grease with butter or coat with nonstick cooking spray

Step 7

Using two forks, deflate the dough by releasing it from the sides of the bowl and pulling it toward the center

Step 8

Rotate the bowl in quarter turns as you deflate, turning the mass into a rough ball

Step 9

Roll the dough ball in the oil to coat it all over, forming a rough ball and move it to the baking pan

Step 10

Let the dough balls rest for 3 to 4 hours depending on the temperature of your kitchen

Step 11

Set a rack in the middle of the oven and preheat it to 425°F /225 C

Step 12

If using the rosemary, sprinkle it over the dough

Step 13

Pour oil over the dough, rub your hands lightly in the oil to coat, then, using all of your fingers, press straight down to create deep dimples

Step 14

Sprinkle with flaky sea salt all over

Step 15

Transfer the pans or pan to the oven and bake for 25 to 30 minutes, until the underside is golden and crisp

Step 16

Remove the pans or pan from the oven and transfer the focaccia to a cooling rack

Step 17

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