Make Dough: Use a scale to measure/weigh flour into a large mixing bowl. Add salt, sugar, and yeast then stir. Add olive oil and water a little at a time while stirring with a dough hook or silicone spoon until well combined. Cover bowl and set it aside for 15 minutes.

Stretch and Fold: Place a small bowl of water next to the mixing bowl. Dip your fingers in the water (to keep dough from sticking to them) and lift an outer section of the dough, pulling up towards the ceiling, and folding and pressing into the center of the dough. Repeat this motion, grabbing a new section of dough each time, moving around the dough until all side have been pulled up and pressed into the center. Cover bowl with a dry kitchen towel and allow dough to rest for 15 minutes.

Repeat this same stretch and fold 3 additional times over the next 45 minutes (this will help strengthen the gluten).

Refrigerate overnight: After the 4th stretch and fold, cover the bowl with a lid of greased plastic wrap and refrigerate overnight (or at least 8 hours). This cold fermentation is essential for flavor and texture.

Add Dough to Pan: Coat the bottom of a 9x13’’ metal pan with 1 1/2 tablespoons of olive oil. Remove dough from fridge and gently transfer to the pan. Gently stretch it to the size and shape of the pan, (it doesn’t need to fit the corners perfectly), careful not to handle it too much.

Rise at Room Temp: Cover pan with a dry kitchen towel and allow dough to rest at room temperature and rise for 2 1/2 to 4 hours. (It should look puffy and have expanded/risen to fill most of the pan. This step will take more or less time depending on your climate and how warm your kitchen is).

Dimple Dough: Preheat oven to 475 degrees F (245 C). Coat your fingers in olive oil. Starting at the short end of the pan nearest you, line hands side-by side and press three (pointer, middle and ring) fingertips gently into the dough until they reach the bottom of the pan, creating dimples throughout the top of the dough. Dimple down one side of the pan and then the other.

Topping: Drizzle 1 1/2 Tablespoons olive oil evenly over the dough; Sprinkle with flakey sea salt (and rosemary, if desired).

Bake focaccia for 20 minutes, until golden. Remove from oven and transfer to a wire cooling rack.