If candied yams are unavailable, regular canned yams can be substituted. The best way to judge doneness is with an instant-read thermometer. The center 2 inches of the pie should look firm but jiggle slightly. The pie finishes cooking with residual heat; to ensure that the filling sets, cool it at room temperature and not in the refrigerator. To ensure accurate cooking times and a crisp crust, the filling should be added to the prebaked crust when both the crust and filling are warm. Serve at room temperature with whipped cream. Vodka is essential to the texture of the crust and imparts no flavor; do not substitute. Any brand of vodka will work, but make sure it is 80 proof (40% alcohol by volume).