Whisk together water, tomato catsup, sugar, corn flour, pounded brown preserved soya beans (or miso), and salt in a bowl to make the sauce. Set aside.

Cut down the backs of the prawns and remove the black intestinal vein. Set aside.

Heat vegetable oil in a wok or shallow saucepan over high heat.

Add the garlic and stir-fry for 1 minute.

Add the chiles and stir-fry for another minute.

Add the prawns and stir-fry until the shell turns slightly red, about 2 to 3 minutes.

Add the sauce and stir-fry until the shells turn red.

Break the egg into the wok and, using a fork, streak the egg through the sauce.

Simmer the sauce for a few seconds and remove from the heat.

Stir in the scallions and lime juice.

Transfer the prawns to a platter, garnish with the cilantro, and serve with chunks of French bread.