Coat the beef with the oyster sauce and two tablespoons each of the fish sauce and brown sugar and massage the mixture into the meat. Allow to marinate for at least an hour or overnight.
To make dipping sauce, toast the rice in a dry pan over medium heat for 10 minutes or until they turn a deep golden brown. Remove from heat and grind in a mortar and pestle. Combine the ground rice with the remaining fish sauce and brown sugar as well as coriander, soy sauce, lime juice, chilli flakes and tamarind. Mix well.
To grill the beef, remove it from the fridge and allow it to reach room temperature. Heat the grill on medium-high and brush with peanut oil. Cook the beef to desire temperature then remove from heat and allow to rest for 3 minutes.
Slice the beef before serving. Serve along with steamed rice.