Combine the chili sauce, ketchup, soy sauce, and sesame oil in a bowl.
Heat a wok or a large deep skillet over medium heat for about 40 seconds. Add the oil, pouring it around the perimeter of the wok to coat the sides and bottom. When the surface shimmers slightly, add the garlic, ginger, chilies, and curry leaves and stir-fry until fragrant and the garlic is golden in color, about 5 minutes.
Add the sauce mixture to the wok and mix well. Allow the sauce to simmer for about 2 minutes.
Add the prawns and stir-fry over high heat, pressing the prawns against the hot wok until they are seared, about 1 minute. Pour in the broth, mix well, and allow the prawns to cook in the broth for about 2 minutes.
Add the egg. Mix and cook until the sauce thickens, about 1 minute more. Remove from the heat. Garnish with the sesame seeds and serve immediately.