Gather the ingredients. In a large bowl, combine the 100 g active sourdough starter, 10 g salt and 430 ml water. Stir with a spatula until mixed (it doesn’t need to be uniform).
Add the 512 g bread flour and mix until fully incorporated. Cover with a cloth and let it rest.
The Fold
After 30 minutes, add 2 Tbsp. extra virgin olive oil and perform some squeezing until it has absorbed the oil. Once you have a smooth ball, fold by reaching into the bowl and pulling the dough up and into the center of the bowl. Turn the bowl a quarter turn and repeat the pulling 8 to 10 times. Cover with cloth and let it rest.
After another 30 minutes, repeat the fold.
The First Rise
Drizzle a splash of oil to prevent sticking. Turn the dough seam side down, cover the bowl with a tea towel cover and let it rise at room temperature for 8 to 18 hours*, depending on your kitchen's temperature and the strength of your starter. Monitor for visual cues (doubling in volume) rather than time. I use an elastic to note the starting point.*Denis's Tip: I usually plan to do this on the day prior so the dough takes the night to raise and I can bake during the next day.
The Baking Pan
When the dough has doubled, pour 2 Tbsp. extra virgin olive oil into a 9x13-inch baking pan.
Drizzle the top of the dough with an additional 1 Tbsp. extra virgin olive oil. Gently deflate the dough and release it from the sides of the bowl using your hand. Scoop the dough into the center of the oil pool in the prepared pan. Fold the dough envelope-style from top to bottom and side to side, forming a rough rectangle. Turn the dough over so the seam side is down. Rub the top with oil.
The Second Rise
Let the dough rise uncovered for 4 to 6 hours or until it is puffy and nearly doubled.
The Baking
Preheat your oven to 425ºF. Using your fingers, dimple the dough. Lightly oil your hands and, using all ten fingers, gently press into the dough to dimple it and stretch it to nearly fit the pan. Sprinkle generously with salt.
Bake at 425ºF for approximately 25 minutes or until golden all around.
The Serving
Remove the pan from the oven and transfer the Sourdough Focaccia to a cooling rack.