In the late afternoons, families and couples flock to the banks of the famous West Lake (Tay Ho), in Hanoi, to enjoy this snack. The vendors compete by creating extravagant pyramids of prawn cakes to entice the hungry customers.

½ cup plain flour

1 tablespoon rice flour

½ teaspoon baking powder

teaspoon ground turmeric

teaspoon salt

pinch of sugar

1 egg yolk

1 teaspoon rice vinegar

10 small raw prawns

2 teaspoons fish sauce

¼ teaspoon freshly ground black pepper

100 g white sweet potato

oil, for deep-frying

vegetable pickle to serve

Sift the plain flour and rice flour into a bowl. Add the baking powder, turmeric, salt and sugar and make a well in the centre. Put the egg yolk, rice vinegar and 250 cm of water into the well and mix to form a paste. Cover the bowl with a wet cloth and set aside for 15 minutes.

Meanwhile, cut off the prawn heads. Leave the shells on and cut the prawns in half lengthways, removing the dark veins. Marinate the prawns in the fish sauce and pepper for 15 minutes.

Peel the sweet potato and cut it into 4 cm strips.

Heat the oil in a wok or a large deep saucepan. Put a metal ladle in the oil to heat up. Spoon 1 tablespoon of the batter into the ladle, add some sweet potato and two prawns and lower it into the oil. When the prawn cake floats, remove it from the ladle and cook until golden brown. Remove the prawn cake with a slotted spoon, drain on paper towel and keep warm while you cook the remaining prawn cakes.

Serve the prawn cakes hot with the vegetable pickle.