Combine the fish sauce with the cane sugar, lime juice and garlic. Coat the meat with the mixture, marinate for approx. 15 mins. Heat a dash of oil in a pan, remove the meat from the marinade, wipe away the marinade, set aside. Brown the meat for approx. 1 min. on each side, season, place on a plate and cover.
Bring the reserved marinade to the boil in the same pan. Remove the pan from the heat, stir in the butter. Cut the meat into strips, serve with the sauce.