If by authentic you mean the kind of momo with *jhol achaar* in, say, Newari restaurants in Basantapur, in Kalimati (Everest momo, for example), or in Haarati, there is none in the area you mention. Take it from someone who has been to several places in those areas. I now make my own momo (which can be a challenge if you are a single bokaa; I have a family).

If, on the other hand, you mean momo with what I like to call fancy achaar -- the kind you get in newer restaurants in K-town (you know the kind they give you in tiny bowls) -- just walk into any Nepali restaurants that claims to serve momo.

HTH.