Our guides from HanoiKids brought us here. We tried the egg coffee, and it was a really unique experience for us. The coffee was really creamy because of the egg yolk used, and the taste and consistency reminded us of coffee-flavored custard. If I lived here, I would probably have this at least once a week! A must-try if you are in Hanoi!
I would recommend that you come with a local, because this place is a little hard to find, and there does not seem to be any English menu. I may be wrong about this though :)