To begin, preheat the oven to 500°F.
Form the flour into a mound on a large work surface and make a well in the middle. Then, add the warm water, salt and olive oil and mix until all of the ingredients are incorporated. Make adjustments, adding more flour or water, as necessary, until the dough comes together.
Knead for 5-7 minutes until the dough is soft and elastic and no longer sticks to the side of the bowl. (Alternatively, you could use a stand mixer fitted with a dough hook attachment.)
Split the dough in half, shape into discs and cover with plastic wrap or a clean kitchen towel and allow them to rest for about 30 minutes.
Once the dough has rested, unwrap one of the discs and using your fingers, press it into a round. Then, using a rolling pin, flatten the dough into a larger circle and stretch it until it is very thin.
Grease the bottom of the pan with olive oil to prevent the focaccia from sticking and then, transfer the dough to the pan, draping the excess dough over the sides.
Smooth the dough across the bottom of the pan to remove any air bubbles. Then, break the cheese into small balls and spread evenly across the dough.
Roll out the top sheet of dough, using the same method you used previously. Drape the dough on top, covering the cheese, allowing the excess to drape over the sides. Press the edges to seal the dough.
Tear holes in the top layer so the cheese will ooze out as it cooks, then, using the palms of your hands, press the dough and cheese into the bottom of the pan.
Run a rolling pin around the edge of the pan to trim the excess dough, drizzle the top with more olive oil and sprinkle with sea salt.
Bake at 500°F for about 15 minutes, or until the cheese is bubbling and the top turns golden.
Remove the focaccia from the oven, transfer to a cutting board. Slice and enjoy!