4 stalks lemon grass, coarsely chopped
1/4 cup vegetable oil
1/4 cup fish sauce
1/4 cup rice wine vinegar
1 teaspoon dark soy sauce
1 teaspoon white sugar
1/2 teaspoon Asian (toasted) sesame oil
4 (8 ounce) beef rib eye steaks (thick-cut)
1/2 cup chopped peanuts
1/2 cup black sesame seeds
1/4 cup sea salt
1/4 cup crushed black peppercorns
1 tablespoon vegetable oil, divided
Place the lemon grass, 1/4 cup vegetable oil, fish sauce, rice wine vinegar, dark soy sauce, sugar, and sesame oil into the work bowl of a food processor, and process until the mixture forms a paste. Coat both sides of the steaks with the marinade paste, and refrigerate, covered, for 2 to 3 hours.
Preheat an outdoor grill for medium-high heat, and lightly oil the grate.
In a bowl, combine peanuts, sesame seeds, sea salt, and pepper until thoroughly mixed.
Remove the steaks from the marinade, and discard any remaining marinade. Pat the steaks very dry with paper towels for good charring. Rub each steak with about 3/4 teaspoon of vegetable oil. Sprinkle the peanut mixture generously over both sides of each steak, and press the spices into the meat.
Grill on the preheated grill until the steaks show grill marks, start to become firm, and are reddish-pink and juicy in the center, 4 to 5 minutes per side. An instant-read thermometer inserted into the center should read 130 degrees F (54 degrees C). Let the steaks rest at least 5 minutes before slicing.