For extra-crackly/crisp crust, add steam to your oven as follows: While the oven is preheating, place an empty cast iron frying pan on the oven rack below the stone. If possible, adjust stone and pan so that the pan isn't directly under the stone, making it easier for steam to reach the baking bread. Once you’ve placed the bread in the oven, pour about 1 cup of boiling water into the cast iron frying pan. Steam will billow from the pan upwards to envelop the baking bread; be sure to wear good oven mitts to shield your hands and arms. Quickly close the oven door to trap the steam.