1 pm (adapt to the time your levain is ready) Mix all the ingredients. The dough will be really sticky but shouldn't feel liquidy. If it does feel liqiudy, add more flour.
After it comes together we're going to knead the dough. If you have a stand mixer you can knead the dough using the dough hook on 3rd speed for 7 minutes or until it starts to unstick from the edges of the bowl. If you knead it by hand you can do it the way you know or use the slap and fold like I did. As you see, it's sticky. Avoid adding more flour as much as possible. Stop after 15 minutes of kneading or when you feel the dough has more resistance and starts to unstick from the table.
Once it's ready, place it in a clean and damp bowl. As you can see in the photo, the dough isn't smooth. Cover it and place it in a warm spot. In my case, that's my oven that's turned off but with the light on. At this point it should be close to 1:15 pm.
1:45 pm Dampen your hands and make 4 folds on 4 sides as if it were a square, to strengthen the gluten. Cover it back up and return it to its warm spot. Repeat the same process at 2:15 and 2:45 pm.
3:15 pm Add about 2 tablespoons of olive oil to the base of your pan. Transfer the dough onto it and pull gently on it to stretch it out. It will shrink back, though! Specially with the oil underneath. Cover it and place it in a warm spot again.
3:45 pm Now that the dough has rested a bit, stretch it out a bit more to fill more of the pan. Cover it and leave it in a warm spot. Repeat this process of stretching it out again at 4:15, 4:45 and 5:15 pm. By the time you do the last stretch, it should fill the pan. Cover and let it proof in a warm spot.
7:15 pm Drizzle about 2 tablespoons of olive oil on the dough.
Use your fingers (with a bit of oil) to make dimples on the dough. You want to make them deep without breaking the dough at the bottom. Sprinkle it with salt, pepper and whatever other ingredient you like.
Bake the focaccia in a preheated oven at 230°C /450°F for 20-30 minutes or until very golden.