This recipe comes from Hugh Acheson, of the restaurants Five & Ten and The National in Athens, Georgia. Acheson: "This soup marries three flavors I love: chestnuts, sherry and porcini. They just work brilliantly together. If you cannot find fresh porcini, use frozen; if you cannot find frozen use dried; if you cannot find dried, use shiitakes; if you can’t find shiitakes you should consider lobbying for better shopping in your neighborhood. You should be able to find chestnuts at your local farmers market if you are located on the East Coast. If not, conventional grocery stores have cans of roasted and peeled chestnuts, just be sure that you do not get water chestnuts."