Preheat your oven to 450°F (230°C) and place a heavy skillet (preferably cast iron) inside.
In a large bowl, sift chickpea flour, pepper, and salt together, then add rosemary leaves.
Whisk warm water and 2 tbsp olive oil into the flour mixture.
Cover the bowl and let the batter set for at least 30 minutes until it reaches the consistency of thick cream.
Stir the sliced onion into the batter.
Remove the skillet from the oven, and add 1 tbsp olive oil to the hot pan.
Pour the batter into the pan and bake for 12-15 minutes or until the pancake is firm and the edges are set (the top may not be browned).
For a finishing touch, set the socca a few inches below your broiler for 1-2 minutes to lightly brown it in spots.
For a finishing touch, set the socca a few inches below your broiler for 1-2 minutes to lightly brown it in spots.