1. In a medium bowl, combine sourdough starter, water, olive oil, and salt and whisk until uniform. 

2. Stir in flour until thoroughly incorporated. The batter will be quite wet and sticky; almost a cross between dough and batter. 

3. Bulk fermentation:  Cover the dough and allow it to rest for 30 minutes at room temperature, then perform a set of “stretch-and-folds,” lifting one side of the dough toward you and folding it back in over itself, then turning the bowl a quarter-turn and repeating this process three more times.* Re-cover the bowl and return it to its resting spot. Over the next two hours, repeat this process three more times, with 30 minutes in between each stretch-and-fold session. After the last one, allow the dough to rest for an additional two hours at room temperature (a total of four hours of bulk fermenting).  

4. Coat the bottom of a 9x13x2″ baking pan, or a jelly roll-sized baking sheet, generously with 2-3 TB olive oil. Don’t be shy with the oil; it may pool on the edges and that’s okay. It’s what gives the focaccia its trademark crispy edges. 

5. Transfer the dough to the oiled pan and flip it to ensure both side are coated with oil. Gently press it toward the edges of the pan, being careful not to deflate it too much. If the dough springs back to the middle, allow it to rest in the pan and try again in a few minutes. It might take several rounds of this for the dough to relax enough to reach the edges of the pan; be patient! It generally takes me about 30 minutes. 

6. At this point, you can proceed to the next step, or cover the dough in the pan and refrigerate it several hours or overnight. This will dramatically slow the rise and further develop the flavor. If you do refrigerate the dough, be sure to allow enough time (2+ hours) to bring it back to room temperature before proceeding. The dough should expand by about one-third of its original size.

7. Dip your fingers in olive oil and poke them all over the top, reaching all the way to the bottom of the pan, to create the focaccia’s signature dimpled appearance. If you haven’t yet mixed the brine, do so now, and pour it all over the dough (don’t worry, it will eventually be absorbed). Cover the dough loosely with a tea towel and allow to rise an additional 2 hours (this is its final proof). 

7. About 30 minutes before the final proof is complete, preheat oven to 450 degrees F. If you have a baking stone, place it on the middle rack of your oven. If not, invert a baking sheet on the bottom rack. 

8. If you’re adding toppings (olives, tomatoes, sausage, etc), gently press them into the indentations throughout the dough. It’s okay if there’s still a little water on top. Drizzle or brush the dough with more (about 2-3 TB) of olive oil, then sprinkle the top liberally with flaky sea salt and any fresh herbs you wish to add. 

9. Place your baking pan atop the pizza stone and bake for 40 minutes. Using a wooden spoon or spatula, carefully check the bottom of the bread. You’re looking for a crisp, deep golden brown color on top and bottom. If the bottom is still pale, bake for an additional 5-10 minutes. 

10. Allow to cool slightly in the pan, then transfer to a baking rack to keep the bottom crust crisp. Cut into slices or squares and serve warm. 

Leftover bread can be wrapped tightly in plastic and stored in an airtight container. To re-crisp the bread, wrap it loosely in foil and heat for 10-15 minutes in a 350 degree oven.