Forget Dairy Queen (which is good). Here is carhop custard served year round by high schoolers on roller skates. Yes, Yearround includes days on which the temperature of the air is colder than the temperature of the custard and there are more frozen flakes between your windshield and the restaurant than in the very generous sized cones and cups.
Watch the menu board for the flavor of the day. When you see chocolate cherry, do not pass go, do not go to the ATM for $200. Turn into the parking lot and order a cone or a quart.