Sieve the chickpea flour in a large bowl. Pour the water, stirring constantly with a whisk.
Add a tablespoon of olive oil, chopped fresh rosemary, salt and pepper to taste. Whisk well then rest at room temperature for 30 minutes, or overnight in the fridge.
When ready to cook the farinata heat a tablespoon of olive oil in a 20cm frying pan.
Whisk the chickpea batter a little and pour half in the hot frying pan.
Cook over medium heat, 5 minutes per side. Cook the remaining batter the same.
Add rosemary and ground black pepper to taste and serve immediately.
Note
Farinata leftovers can be kept in the fridge for a few days. Heat them in the oven before serving.