This small guanz (canteen), with plastic tablecloths and bare walls, may not have much atmosphere, but it's well known for serving some of the best buuz in the city (nearly homemade quality). Unlike most other cafes, the dumplings here are not overly fatty and come piping hot from a special steamer. Try a few with süütei tsai (Mongolian milk tea with salt).
Look for the picture of the two kids gorging on a big plate of buuz.