Shrimp and Sweet Potato Fritters

Golden orange and crispy, this Hanoi specialty blends the fragrance and crunch of sweet potatoes with the brininess of shrimp. The fritters, which look like roughly formed nests on which whole shrimp rest, are cut into bite-sized pieces and bundled in lettuce with fresh herbs and cucumber. My mother taught me to soak the potatoes with a bit of slaked lime (calcium hydroxide), which Southeast Asian and Indian cooks use to crisp ingredients for frying and pickling. It is basically moistened food-grade slaked lime powder, the same compound used to treat corn for making Mexican masa. The Vietnamese call it voi and it is sold in small, round plastic containers in Chinese, Thai, and Viet markets, usually stocked in the flour aisle. Two varieties are available, red and white. I prefer the white one, though the red one, which has been colored by the heartwood of the cutch tree and is traditionally chewed with betel leaf, may also be used. A small container of slaked lime lasts for a long time because only a little is needed.