How to Make It
With a meat pounder, pound the meat between 2 sheets of plastic wrap until you have wide, thin strips. In a shallow bowl, combine the soy sauce, sugar and sake; stir to dissolve the sugar. Stir in the remaining ingredients. Add the meat and turn to coat with the marinade. Set aside to marinate for 1 hour, turning the meat from time to time.
In a medium bowl, combine the soy sauce, sake and sugar; stir to dissolve the sugar. Add the Asian pear, scallions, onion and sesame seeds. Pour the sauce into 6 small bowls.
Light a grill. When the fire is hot, arrange the meat on the grill and cook for 1 to 2 minutes per side, or until nicely browned. Transfer the meat to a platter and arrange the romaine leaves alongside. To eat, wrap a piece of meat in a lettuce leaf, dip the bundle in the Asian pear sauce and pop it into your mouth.