Combine flour, kosher salt, sugar, and yeast and mix well
Add water and 2 tablespoons of your olive oil to dry ingredients and use a dough whisk or another stiff utensil to mix until a wet loose dough forms and no big flour pockets remain. Cover and allow to sit for 15 minutes.
After resting the dough, you will fold it to strengthen the gluten and develop an airy crust.
Starting at the twelve o’clock 🕛 position, use a slightly wet hand, or a flexible dough scraper, to grab the edge of the dough, pull it toward the center, and over to the other side of the dough.
Turn the bowl a quarter turn and do it again, and continue until you’ve done four folds, all the way around the dough.
Cover the dough again and allow it to rest for 5 minutes. Repeat the folding technique 2 more times (for a total of three times) 5 minutes apart.
Overnight proofing: Spray your baking pan with a little bit of nonstick spray and then add 2 more tablespoons of your olive oil to the bottom of the pan. Transfer your dough to the pan, cover, and refrigerate at least 8 hours, up to 12 hours.
In the morning: Remove your baking pan from the refrigerator and allow the dough to come to room temperature while you preheat your oven to 450°F and place the rack in bottom third of the oven.
To make the (optional) topping: Strip the rosemary from the stems and chop. Using a fine zester, grate the garlic. Add rosemary, grated garlic, and ½ teaspoon kosher salt to the final 2 tablespoons of olive oil and mix well.
Spoon the rosemary garlic olive oil all over the surface of the dough and gently spread around. With your fingertips, press deeply into the top of the dough, almost to the bottom, to make the traditional dents found on the surface of focaccia.
Bake on the bottom rack of your oven for 25-30 minutes or until the top is golden brown.
Remove from the oven and brush the top with a little more olive oil and sprinkle with flaky sea salt, if desired. Removed from the pan and allowed to cool on a wire rack until ready to eat.