Yaki imo

Roasted sweet potato is a popular winter street food in East Asia. In China, yellow-fleshed sweet potatoes are roasted in a large iron drum and sold as street food during winter. They are called kǎo-báishǔ in northern China, wui faan syu (煨番薯) in Cantonese speaking regions, and kǎo-dìguā (烤地瓜; "roasted sweet potato") in Taiwan and Northeast China, as the name of sweet potatoes themselves vary across the sinophone world. Sweet potatoes roasted in drum cans, called gun-goguma (군고구마; "roasted sweet potato"), are also popular in both North and South Korea. The food is sold from late autumn to winter by the vendors wearing ushanka, which is sometimes referred to as "roasted sweet potato vendor hat" or "roasted chestnut vendor hat". Although any type of goguma (sweet potato) can be roasted, softer, moist varieties such as hobak-goguma (pumpkin sweet potato) are preferred over firmer, floury varieties such as bam-goguma ("chestnut sweet potato") for roasting.

Source: Wikipedia