1-In a large bowl, whisk together 4 cups (512 g) of all-purpose flour or bread flour, 2 to 3 teaspoons (10 to 15 grams) of kosher salt, and 2 teaspoons (8 g) of instant yeast. Add 2 cups (455 g) of lukewarm water and mix with a spatula until the ingredients form a sticky dough ball. Lightly rub the dough surface with a portion of the 4 tablespoons of olive oil, then cover with a damp towel, cloth cover, or plastic wrap and refrigerate immediately for at least 12 hours and up to 3 days. For a quicker option, let the dough rise at room temperature until doubled in size, about 1.5 to 2 hours.

2-Grease the pans with butter and add 1 to 2 tablespoons of olive oil to each pan.

3-Deflate the dough using two forks, divide it if using multiple pans, then roll the dough balls in the oil to coat. Place the dough in the prepared pans and let it rest at room temperature for 3 to 4 hours, or until it appears puffy.

4-Preheat the oven to 425°F with the rack in the middle position. If using, sprinkle 1 to 2 teaspoons of whole rosemary leaves on top. Drizzle the remaining olive oil over the dough, then press your fingertips into the dough to create deep dimples all over. Sprinkle flaky sea salt evenly on top.

5-Bake for 25 to 30 minutes, or until the focaccia is golden and crisp on the bottom. Remove from the oven and transfer to a cooling rack. Let it cool for at least 10 minutes before cutting, or longer if preparing for sandwiches. The recipe yields 2 loaves.