In a large mixing bowl, whisk together 4 cups of all-purpose flour, 2 teaspoons of kosher salt, and 2 teaspoons of instant yeast.

Gradually add 1 and 3/4 cups of lukewarm water to the flour mixture and stir until a sticky dough forms.

Cover the bowl tightly with plastic wrap and let it rest for 30 minutes.

Wet your hands and stretch and fold the dough in the bowl 8 to 10 times.

Drizzle a tablespoon of olive oil over the dough and gently turn it to coat, then refrigerate for 12 hours to 3 days.

Grease two baking pans with butter or olive oil and pour an additional tablespoon of olive oil into each pan.

Remove the chilled dough, deflate it, and shape it into two round balls.

Place the dough balls in the pans, cover with a kitchen towel, and let them rest at room temperature for 3 to 4 hours.

Preheat your oven to 425°F (220°C) about 20 minutes before baking.

Dimple the surface of each dough ball, drizzle with olive oil, and sprinkle with rosemary and flaky sea salt.

Bake for 25-30 minutes or until golden brown and hollow-sounding when tapped.

Let the focaccia cool on a wire rack for at least 10 minutes before slicing.