Start with the batter: In a bowl, combine flour and a pinch of salt. Create a well in the center, add the olive oil, then gradually incorporate 15 cl of lukewarm water, stirring with a spatula until smooth. Refrigerate for 2 hours to rest.
While the batter chills, make the tartar sauce: Mash the boiled egg yolks with mustard using a fork. Slowly drizzle in the sunflower oil while whisking vigorously to emulsify. Stir in the chopped herbs, capers, and coarsely chopped gherkins. Season to taste.
Just before frying, gently fold the beaten egg white into the batter. Heat sunflower oil to 180°C (350°F). Line a baking dish with paper towels and preheat the oven to 180°C (thermostat 5).
Remove the heads from the prawns. Dip them in the batter, then fry in small batches in the hot oil for 3-5 minutes, depending on size, until golden and crisp. Drain on paper towels and keep warm in the oven until all are cooked.
Serve the hot scampi on a platter, garnished with lemon slices and parsley sprigs. Pair with the tartar sauce and enjoy immediately for the best flavor and texture.
