Sweet pea pudding is made from yellow pea flour, sugar, and water and like many Beijing street food snacks, its heritage can be found in the history of the royal family presiding over China at any given time. Wandouhuang was a favorite with members of the royal family during the Ming dynasty, however, it can now be found at local supermarkets, particularly Beijing cuisine restaurants, or the famous Daoxiangcun Bakery.
Update: June 23, 2021