Prepare the prawns (see
Dry-fry the black sesame seeds in a small pan for 1–2 minutes or until they are fragrant, then set them aside.
Heat the oil in a wok or large frying pan and stir-fry the garlic over a medium heat until it is lightly browned.
Add the prawns, water chestnuts and mangetout and stir-fry over a high heat for 1–2 minutes. Add the stock, soy sauce and oyster sauce and stir-fry for another 2–3 minutes or until the prawns open and turn pink. Stir in the fried sesame seeds and serve immediately.