At a glance, chả rươi looks like a typical omelet or an eggy pancake of some sort. Served with a side of fish sauce and vegetables, it entices diners with its browned edges, irresistible fragrance, and meaty-looking texture. However, there is one main ingredient in chả rươi that you wouldn’t expect: sandworms.

Also known as the sandworm omelet, chả rươi is a rare Vietnamese dish that is popular in the North, especially Hanoi. It’s uncommon even among locals because the worm, which dwells in northern wetlands, can be found only in the fall. For the rest of the year, frozen sandworms can be used, but the best chả rươi uses fresh ones.

Most of the sandworms come from farmers who sell to Hanoi and China. Prior to cooking, cooks must first rinse the worms in hot water to remove their tentacles. The worms are then mixed with eggs, citrus peel, onions, dill, ground pork, and spices, and then fried until brown. Hearty and high in protein, it is a favorite cold-weather dish.