Mix all the mayo ingredients together in a small bowl and set aside. Mix all the ingredients for the batter, except the sparkling water, in a large bowl. Whisk in the water to form a loose batter. Wash then pat the prawns dry with kitchen paper and set aside.

Heat a 10cm depth of oil in a deep-fat fryer to 180C or pour into a large, deep pan, ensuring it is no more than a third full. Test the temperature using a thermometer or drop some batter into the hot oil – it is ready when it turns golden in just under a minute. Do not leave the pan unattended.

Dust the prawns in flour to coat evenly and shake off the excess. Dip the prawns into the batter, then lower them carefully into the hot oil and deep-fry for 2-3 mins until golden and crisp. You will need to fry in batches and allow the oil to come back up to temperature in between. Carefully remove the prawns using a slotted spoon and drain on a tray lined with kitchen paper. Repeat with the remaining prawns. Meanwhile, split the buns and toast the cut side, if you like. Dust the battered prawns with a pinch of paprika and season with salt. Serve in the buns, on the lettuce with the spiced mayo drizzled over, plus extra on the side, and lime wedges for squeezing over.