Ho Tay (West Lake) in Hanoi is where these delicious fritters originated. A banh tom Ho Tay is a sweet potato shrimp cake made with fresh water shrimp from Ho Tay. Nowadays, you can find banh tom all over Vietnam, but the shrimp used won't likely be from West Lake.
Sweet potato is shredded up and mixed with a flour batter. A whole shrimp is placed on top and the fritter is deep-fried in oil. When I say 'a whole shrimp', I mean a whole shrimp - head included. The Vietnamese eat the shell, tail, and head. This might seem off-putting, but the crunchiness of the shell adds to the overall texture of the dish. Or at least that's what I'm told. I'll admit that I haven't quite gotten over the crunchy texture of a shrimp's head, but my Asian friends often declare, "It's the best part".
Wrap your fritter in lettuce, dip it in nuoc mam cham, and take a bite. The sweetness from the potato is balanced by the oil. It goes great with beer, and they'll stay nice and crispy for hours.