Soufflés—savory and sweet mixes lightened with an egg-white foam, then dramatically inflated above their dish by oven heat—have the reputation for being difficult preparations. Certainly they can be among the most delicate, as their name—French for “puffed,” “breathed,” “whispered”— suggests. In fact, soufflés are reliable and resilient. Many soufflé mixes can be prepared hours, even days in advance, and refrigerated or frozen until needed. If you manage to get any air into the mix, an inexorable law of nature will raise it in the oven, and opening the door for a few seconds won’t do it any harm. The inevitable post-oven deflation can be minimized by your choice of ingredients and cooking method, and can even be reversed.