In a smoking hot fry pan or wok, add the vegetable oil and lemongrass and cook until fragrant, then add the garlic and chiles.
Now add the beef and stir fry for 2 minutes, then season with the fish sauce, soy sauce, and sugar. Add the betel leaves and stir fry for a further minute.
Transfer the mixture to a plate and garnish with sliced chile and coriander (cilantro).
Serve with steamed jasmine rice.
When dicing the lemongrass, always use a nice heavy sharp knife. If you have a second knife, use the two simultaneously. Do not discard the tips of a lemon grass stalk, steep it in hot water and drink it as lemon grass tea.