my favourite :)
Hu guo si restaruant (护国寺小吃). It's a chain restaurant where supplies traditional beijing food.
But I think only beijinger can accept this taste...
have you guys tried 豆汁 dou zhi？that is the watery remains of the same process where this Ma Dou Fu is the other come out (the main product is starch of green beans). Both Dou Zhi and Ma Dou Fu are typical Beijinger Food.
I like it~