In a large bowl, weigh out the water, ensuring it is warm but not too hot.
465 g Water
To that bowl, add your stater. Mix using a Danish dough whisk until the starter has mixed into the water and its cloudy and a little foamy.
140 g Starter
Add the bread flour and mix until there are no visible dry spots.
600 g Bread Flour
Cover with plastic wrap and let rest for 1 hour.
At this stage, feed your starter and either leave it on the counter if you're planning to bake again, or leave on the counter for 1 hour then place in the fridge.
Adding Salt
Sprinkle the salt on the top of the dough, and using your fingers, thoroughly poke the dough to push some of the salt in. Perform 'stretch and folds' until the salt is totally incorporated.
20 g Fine Salt
Perform 2 sets of coil folds to shape the dough into a ball-like shape.
Recover and allow to rest for 30 minutes.
Coil Folds Series
Perform 3 sets of coil folds, 30 minutes apart. After each set of coil folds, do your best to have the dough is a ball-like shape, recover and allow to rest until it is time for the next set.
Bulk Fermentation
After your last set of coil folds, transfer the dough to a straight-sided container that is at least 2.5x the size of the dough.
Mark the top of the dough with an elastic band or some other indicator so you know when it is proofed.
Cover and leave on the counter until it has more than doubled and has visible bubbles on the top and sides.
At this point, you should be able to gently touch the top of the dough without it sticking to your finger.
Final Prep and Proof
Preheat your oven to 425℉.
Drizzle ¼ cup of olive oil in a deep 9x11 metal baking pan.
Turn out your dough into the pan. You want what was the top of your dough while proofing to also be the top of your dough when baking. Therefore, if you were unable to flip your dough while turning it out, very gently flip it over now.
Using a spoon, take some of the olive oil in the pan and pour it over the top of the dough. Allow this to go through a final proofing for 20-30 minutes or until the dough has expanded to all side and nearly filling out the corners.
Dimpling and Baking
Sprinkle the rosemary across the top of the dough and sprinkle with flaky salt.
2 sprigs Rosemary
Maldon Salt
Dip your fingers in the olive oil and gently but thoroughly dimple the dough, allowing your fingers to reach the pan while moving them in a slightly circular motion.
If there are any dimples that are noticeably void of olive oil, drizzle a little on top.
Place the pan on the middle rack and allow to bake for 25-35 minutes or until golden brown on top.
Once done, place the focaccia on a wire rack and allow to cool completely.