Lan Fong Yuen claims to have invented Hong Kong–style milk tea: a blend of black teas and evaporated milk that is filtered through a sackcloth bag (the look of which after sustained use gives rise to the tea's nickname: "silk stocking" milk tea).
There are a few branches around Hong Kong, but the original is in Central. It's a typical cha chaan teng—a traditional "tea restaurant" serving instant noodles, buns, toast, and, of course, milk tea. However, the entrance is hidden by a kind of shack or wooden stand, presumably to regulate the flow of customers desperate to sip a little history.
Luckily, takeout is available, and the line moves quickly. Just make sure to join the right line, as one of them is for entrance to the cafe itself, which is one-in-one-out.
As for the tea: It's good. Strong and yet extremely silky, and with a kind of umami mouthfeel. Probably not worth a special trip unless you're a real enthusiast, but definitely worth the wait if and when you find yourself nearby.