3-1/2 cups (or 420g) all purpose flour
1-1/2 cups (or 360g) water
100-150g active sourdough starter (fed)
1 tbsp coarse kosher salt
olive oil
The night before, feed your starter as you normally would and let it sit out on the countertop.
The next morning, in a large mixing bowl, add the active sourdough starter, water, and salt. Mix until the starter is evenly dispersed and no clumps remain.
Add the flour and mix until no clumps of dry flour remain. The mixture should look something like what I show in the video - a wet, sticky dough mass. If it looks too wet, feel free to add a little more flour.
Cover with plastic wrap and let rest for 30 minutes.
For the next 4 hours, every 30 minutes, perform one set of stretch and folds (1 set is a stretch, fold, quarter turn the bowl, repeat 4 times). Cover with plastic wrap and let rest after each set.
After the last set, cover with plastic wrap and let rise for 1-2 hours.
Prepare a 9"x13" baking tray with raised walls by drizzling olive oil.
Transfer the dough from the bowl into the tray. Using your hands, roughly spread the dough to fit the shape of the tray. Then to shape, fold in all four sides of the dough towards its center. Spread the dough out again to roughly fit the shape of the tray (it's okay if it doesn't fill the corners - as it rises, it will). Cover and let rise for another hour or until doubled.
Preheat the oven to 425F.
Uncover the baking tray and drizzle the top with some olive oil. Oil your fingers and dimple the dough. Don't be afraid to aggressively dimple the dough since this will give the focaccia its signature look.
Bake for 20-25 minutes until the top is golden brown.
Optional - add some flaky sea salt on top of the focaccia while it's still hot out of the oven. Let cool 20 minutes before slicing and enjoy!