Add 2 1/2 TBSP olive oil in an 8-inch cast iron skillet. Place in the oven and preheat to 450°F. You want the oil to heat as the oven does so the oil and pan both get hot.
Whisk together all the ingredients until combined. Carefully remove the skillet from the oven and pour the batter into the skillet, swirling around as you do so. The batter should coat the bottom of the skillet evenly.
Bake the socca for 15-17 minutes until crispy. Flip once removed from the oven to give the other side a bit of crisp as desired. Sprinkle on additional sea salt flakes and serve warm.
If you use a bigger skillet, the flatbread will cook quicker and will likely be crispier (the opposite will be true for a smaller pan).