Mix steamed rice with a couple of pinches of salt. Make a tight cylindrical ball 1/2 cup (or little less for smaller Onigiri) steamed rice, about three inches long. Repeat to make 4-5 rice balls. Wrap each rice ball with one paper thin slices of beef so that there is no rice exposed.

In a small bowl, mix Soy Sauce, Sake, Mirin, sugar and water.

Heat oil in a frying pan at medium heat, and cook wrapped rice balls until the beef is browned all around. Add sauce to the pan, coating the beef, and cook until almost all the liquid is gone.

Sprinkle with sesame seeds and serve with lettuce leaves.