Mix the starter and water in a large mixing bowl or bowl of a stand mixer. Rest 5 minutes. Mix the flour with the starter, water, and rest of the ingredients except for olive oil. Mix and knead by hand or stand mixer with the dough hook until the dough comes together and is smooth. 10-15 minutes. Place the dough in a bowl that's been lightly oiled, cover, and rest for 50-60 minutes.
Fold the dough over itself, pulling from the bottom over the top three or four times rotating clockwise after each fold. Rest another 60 minutes.
Drizzle and spread 3 Tbls olive oil onto a standard half sheet pan. Turn out the dough on the pan, and turn it to coat it with the oil. Stretch the dough into the edges of the pan. Cover it with a clean towel, and let it rest for 10 to 15 minutes. Gently stretch the dough again so it dough fills the pan as much as possible. Cover with plastic wrap and refrigerate for 12 to 14 hours overnight.
The next day, preheat the oven to 425°F and the focaccia sit out for 30-45 minutes before baking. Before baking, firmly dimple the top of dough with your fingers, but not too much. You don’t want to lose all the gasses in the focaccia. Drizzle the top with olive oil to collect a little in the dimples and top with any herbs and a bit of sea salt.
Bake the focaccia for 20 to 30 minutes till golden brown. Remove from the oven. Allow it to cool 10 to 20 minutes before removing from the pan.