HANOI, June 12 (Xinhua) -- Pia is a specialty cake in Vietnam, which is made of wheat flour, green beans, durian and salted duck eggs. It first appeared in the southern province of Soc Trang in the 17th century, when Chinese people migrated to Vietnam's southern region, bringing the cake as a reserve food during their hard long journey. Nowadays, there are several large and old bakeries with more than 30 years in the province, making the cakes for both domestic and foreign markets.