Step 1

Place the flour, salt, and yeast in a food processor fitted with the blade attachment and pulse to combine. Add the water and 2 tablespoons of the oil. Pulse until a rough ball of dough forms, about 15 (2-second) pulses.

Step 2

Drizzle 2 teaspoons of the oil in a large bowl. Flour your hands, scoop the dough out of the food processor, and form into a smooth ball. Place the ball of dough in the oiled bowl and turn it so it's coated on all sides. Cover with plastic wrap or a kitchen towel and let it sit at warm room temperature until doubled in size, 2 to 3 hours.

Step 3

Drizzle 1 teaspoon of the oil in a 10-inch cast iron or other ovenproof skillet and rub it over the bottom and sides. Punch down the dough and place the dough in the skillet. Using your fingertips, coax and stretch the dough to cover the bottom of the skillet and reach all the way to the edges. Cover with plastic wrap or a kitchen towel and let rest at warm room temperature until puffed and slightly risen, 30 to 40 minutes. Meanwhile, arrange a rack in the middle of the oven and heat to 450°F.

Step 4

Use you fingertips to gently dimple the surface of the dough. Drizzle the remaining 1 tablespoon of oil over the dough so that it pools in some of the indentations. Sprinkle with the rosemary and flaky salt.

Step 5

Place in the oven and immediately turn the heat down to 400°F. Bake until lightly golden-brown, 20 to 25 minutes.

Step 6

Remove from the oven and cool for at least 15 minutes before slicing and serving. Focaccia is best eaten when warm, but is also good at room temperature. If the crust gets too soft, reheat in a 350°F oven to crisp it up.