Pre-heat the oven to 250 degrees C, or as hot as your oven will go. Use about 5 or 6 tablespoons of oil in the pan and heat it up in the oven.
Pour the cold water into a pot and use a whisk to mix in the chickpea flour, olive oil and salt, beating thoroughly to remove any lumps. Add the rosemary now if you are using it. If the mixture is to thick, add a little more water. It should be similar to a crêpe mix.
Remove the pan from the oven and pour out the batter, covering the pan evenly. Be mindful that the oil will splatter.
Place the pan back into the oven and cook until the top browns nicely, approx. 15 to 20 mins, or longer depending on your oven and the pan used.