In a large bowl with lid, add half of the water to the flour and mix. Then add the ramaining water with the sourdough starter/levain and salt. Mix until a very rough dough forms. Cover and let it rest for 30 minutes.
After 30 minutes, dust your work surface with flour and tip your dough on it. Then fold it 4 times: start with stretching it away from you and fold it back, then flip it 90 degrees and repeat three more times. This folding process help developing the formation of the gluten without having to knead it. Cover the dough with the bowl and let it rest for another 30 minutes.
Repeat 2 more sets of folds, 30 minutes apart. At the end of the last set, put it back into its bowl, cover and let it proof overnight in the coolest section of your fridge (usually where the fruit and veg is).
The day after, after a 12-24h rest in the fridge (depending on the temperature and the strength of the flour used) the dough is ready to be shaped and baked.Take it off the fridge 30 minutes before, to allow it to come back to room temperature. Preheat your oven to 230°C or 446° Fahrenheit.
Take a large oven tray (mine is roughtly 44x37cm) and line it with lightly oiled parchment paper. Tip your focaccia dough on it and using the tip of your fingers, stretch the dough into a rectangular shape. You don't have to be accurate for this step.
In a small bowl, mix 2 tablespoons of olive oil with 2 tablespoons of water and pour it onto the focaccia dough. Then press your fingers into the dough to make dimples. Sprinkle with a bit of sea salt flakes and then put the tray at the bottom of your oven. Bake for 20 minutes.
While the focaccia is baking, prepare your topping: mix vigorously the grated Pecorino Romano, the two eggs, salt and pepper until well combined.
After 20 minutes, take the focaccia out of the oven and pour your egg and cheese mix on it. Put it back in the oven for 5 more minutes.
Lastly, take the focaccia out of the oven for one more time to lay the pancetta slices on top of it, then bake for an additional 5 minutes or until crisp.