Puree all marinade ingredients (soy sauce, cilantro, lime zest, lime juice, fish sauce, oil, sugar and garlic) with a hand mixer or food processor until it forms a paste.
Combine marinade and beef in a non-reactive container and marinate in the refrigerator for four hours.
Thread the beef strips onto pre-soaked bamboo skewers.
For the dipping sauce, combine all ingredients (sour cream, cilantro and lime juice) and refrigerate until ready to serve).
Preheat a charcoal grill to medium-high heat, about 350-400 degrees.
Grill the skewers for three minutes on each side or until char marks form. These are thin slices of meat so they don’t need much time on the grill.