Whisk the garbanzo flour, water, olive oil and salt together in a jar or bowl. Cover with a cloth and rest. The socca is best when the garbanzo bean/chickpea flour has an opportunity to soak for at least a 1/2 hour, but overnight is ideal. We like to keep the batter in a jar on hand for dinners for a few days.
Once the batter has rested and you are ready to cook it up, heat a cast iron pan, metal pie dish or similar in an oven on broil. Alternatively, place the cast-iron skillet on high on your stove, or on high on your grill. The hotter the better at least to start.
Once the pan is piping hot, pull out the skillet and drizzle in a splash of the oil (more if your pan tends to stick). Pour in the batter gently and swirl it around until it thinly fills the pan. Place it back in the broiler, stove, or grill and roast until the edges start to dry out and the center is no longer wet. Dark marks are completely fine.
Loosen the pancake with a thin spatula and flip over. Return the heat for about 30 seconds up to a minute. Flip back over and cut immediately into wedges or in semi-squares.
It is tastiest when piping hot. Leftover socca is also ideal when warmed before serving.
Trouble-shooting:
Is it sticking? Your pan may not be seasoned enough and the next socca could use more oil. Or sear it longer, once it is well cooked and quite dark it will loosen from the pan more easily.
Taste the first socca, add more olive oil for flavor or salt as needed to the batter.