I used to work at a DQ and our shakes were made from the same "mix" as our regular soft serve. It was just frozen as much as the soft aerve. We also made a lot of shakes with just the soft serve and milk. So if you find a recipe similar to their "ice milk" and can use that... if not, find an ice cream that you like and mix it with milk. Maybe 1/4 milk to 3/4 ice cream