The "buttery" nature of it could have been the kind of milk that was used -- one consequence of freezing high-fat milk quickly is that the fat will tend to "cra

The "buttery" nature of it could have been the kind of milk that was used -- one consequence of freezing high-fat milk quickly is that the fat will tend to "crash out" of emulsion (this is a side-effect of the same phenomenon that makes the ice crystals smaller). So you'd want to use a leaner mix. If your teacher used half-and-half or cream, the resulting ice cream was probably pretty fat-forward on the tongue. (Aside: I've seen this demo done by a bunch of different people, and I'm always a little disappointed by the level of science involved. Usually, it's little more than "See? Liquid nitrogen is REALLY COLD". That's fine, I guess, but there's much more interesting stuff going on!)