Prepare the chickpea batter. Whisk the chickpea flour, water, olive oil, and salt together in a medium bowl until smooth. Let rest for 30 minutes to give the flour time to absorb the water.

Preheat the oven and then the pan. Arrange an oven rack 6 inches below the broiler element and heat to 450°F. About 5 minutes before the batter is done resting, place a 10-inch cast iron skillet in the oven and turn the oven to broil.

Add the batter to the prepared pan. Carefully remove the hot skillet from the oven. Add about 1 teaspoon of oil, enough to coat the bottom of the pan when the pan is swirled. Pour the batter into the center of the pan. Tilt the pan so the batter coats the entire surface of the pan, if needed.

Broil the socca for 5 to 8 minutes. Broil until you see the top of the socca begin to blister and brown, 5 to 8 minutes. The socca should be fairly flexible in the middle but crispy on the edges. If the top is browning too quickly before the batter is fully set, move the skillet to a lower oven rack until done.

Slice and serve. Use a flat spatula to work your way under the socca and ease it from the pan onto a cutting board. Slice it into wedges or squares, sprinkle with salt and pepper, and drizzle with more olive oil and sprinkle with the za’atar if using.