Gather all ingredients.

Stir yeast into 4 cups plus 2 tablespoons bread flour in a large bowl. Add salt, followed by 4 teaspoons olive oil. Pour in water. Stir with a spoon until a wet, sticky dough forms.

Cover and let sit at room temperature for 12 to 14 hours.

Uncover dough and transfer to an oiled work surface. Using oiled hands, press and push dough into a 16x12-inch rectangle.

Fold dough into thirds horizontally; fold vertically into thirds. Transfer dough to a generously oiled pan, smooth-side up.

Cover the pan with plastic wrap and let rest until almost doubled in size, about 1 hour.

Remove the plastic wrap. Using oiled hands, fold once more into thirds horizontally, then into thirds vertically to develop gluten structure.

Flip dough, smooth-side up on the pan; cover with plastic wrap and let rest for 1 hour more.

Remove the plastic wrap. Stretch and fold dough once more in each direction using oiled hands.

Transfer, smooth-side up, into a generously oiled metal baking pan. Lightly drizzle with additional olive oil and stretch to fit the pan. Cover and let rest for 2 hours.

Preheat the oven to 425 degrees F (220 degrees C). Uncover and poke holes in the top of dough with oiled fingers, if desired, for the traditional focaccia look. Sprinkle the top with rosemary and flaky sea salt.

Bake in the center of the preheated oven until browned, about 30 minutes. Let cool in the pan for 10 minutes; transfer to a wire rack and let cool to room temperature, about 30 minutes.

Slice and serve.