They just use normal black tea, I think, but then add milk (possibly yak), and yak butter to it. They then churn it in something that looks too much like a toilet brush in one of those cylindrical holders so the end product tastes exremely buttery but barely has any signs of oil on the surface. the place is on the same latitude as morocco, I guess, but even in summer it get's cold up that high, so they don't worry about getting fat! It's a good way of getting more calories when there's little meat around.