The recipe looks great, can't wait to try it. As far as the "real" recipe used by Universal, of course it can't have dairy because it needs to last a long time without spoiling and possibly being kept at uneven/warm temperatures occasionally. I've read several reviews (including one by the Leaky Cauldron) that stated the foam kept replicating itself in the glass, and might contain yeast. As you drink more and more butterbeer, the foam actually increases in size. Since the base liquid isn't carbonated, people are guessing that the foam contains yeast. Yeast and a lot of different forms of sugar, that's my guess for the real recipe!