One of my favourite dishes in Viet Hoa is the beef skewers with wine and herbs. It took me a while to find a marinade that recreated them perfectly, but here it is:
750g beef fillet
3 cloves garlic crushed
1 stalk lemon grass
1 small red chilli finely chopped
1 teaspoon caster sugar (brown is better)
1 tablespoon fish sauce (get vietnamese nuoc mam if you can)
2 teaspoons rice wine vinegar
1 tablespoon soy sauce
1 teaspoon sesame oil
Put the beef in the freezer while you make the marinade.
You can chop the lemon grass if you like, but I prefer to slice the very end off, so you can see the white middle, and cut long slits down the length of the stalk, but leaving about an inch intact at the top. Then you can bash the bulbous bottom end with a mallet or a flat heavy knife to release the flavour, but the stalk remains in one piece that you can remove it easily at the end of marinading or cooking.
Mix all of the marinade ingredients together in a large bowl.
Slice the beef very thinly and marinate for at least 4 hours, but preferably overnight (cover the bowl with cling film).
Thread the beef onto skewers and cook on a hot barbecue or griddle. If you like you can sprinkle them with sesame seeds before cooking, and serve with coriander leaves.