In her memoir “The Year of Magical Thinking,” Joan Didion wrote that she learned to make soufflés, one of her signature dishes, while living in Southern California in the early 1970s. “The trick,” he concluded, “was a less rigorous approach than generally recommended.” This fall version, taken from a handwritten and well-stained card in his archives, doesn’t puff up as impressively as a classic French soufflé, but the beaten egg whites lend a delicate touch to the dense sweet potatoes. Their sweetness is pleasantly tempered by the butter and lemon zest. —Patrick Farrell
