Fried pork liver (炒肝，Chao-Gang). It is a dish either you love it or hate it. It is actually boiled, not fried. But in the boiling process, the chef needs to stir it frequently, which looks like frying it.
The history of it can be traced to Song Dynasty (960-1279), when it was a cheap dish for the poor.
Ingredients: pork livers, lungs and intestines served in a thick broth with minced garlic
Taste: salty, chewy, a little spicy from the garlic
Price: 5 Yuan (80 cents)
Where to have it: Yao's Chaogan, a local restaurant just around the corner from Drum Tower at Gulu dajie. As Tianning recommended, you can also have baodu (Boiled tripe) there.
Address： ＃311 Gulou East Street Dongcheng, Beijing, China
Resource and more info: http://goo.gl/CFKL0
Nearby places of interest: The drum Tower, The bell Tower and Houhai area
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Interestingly, the U.S. vice president Joe Biden visited this restaurant and only bought noodles and baozi(Steam bums), which, by the way, are also popular, during his visit to Beijing in 2011. It looks like it takes guts to try
this local speciality-"Fried pork liver".
Tianning's recommedation on where to have Fried Pork Liver.