The company whose OG sign said "McDonald's Famous Hamburgers" the year they introduced "fast food" principles into their operations was actually built around shakes?
Ray Kroc (who is really responsible for the growth of the McDonald's franchise) was a milkshake machine salesman. I believe he was introduced to the McDonalds brothers when selling them a milkshake machine that could mix multiple individual milkshakes at once.
Edit: here's the "multimixer": http://www.sterlingmulti.com/multimixer_history.html