Bool kogi is eaten like moo shu or fajitas, using lettuce instead of a pancake or tortilla.
Step 1: If using tenderloin tips, butterfly them to obtain broad flat pieces of meat; each should be about 4 inches long and wide and 1/4 inch thick. If using sirloin, cut it across the grain into 1/4-inch slices. Whichever cut you use, using the side of a cleaver or a rolling pin, pound the slices between two sheets of plastic wrap to flatten them to a thickness of 1/8 inch. Place the meat in a large nonreactive baking dish and set aside while you prepare the marinade.
Step 2: Combine the soy sauce, sugar, sake, sesame oil, garlic, scallions, sesame seeds, and pepper in a small bowl and whisk until the sugar dissolves. Pour the marinade over the meat in the baking dish and toss thoroughly to coat. Let marinate in the refrigerator, covered, for 1 to 2 hours.
Step 3: Set up the grill for direct grilling and preheat to high.
Step 4: When ready to cook, brush and oil the grill grate. Add the garlic kebabs (if using) to the hot grate and grill for 4 to 5 minutes. Then arrange the pieces of meat on the grate and grill, turning with tongs, until nicely browned on both sides, 1 to 2 minutes per side. Turn the garlic kebabs as the meat cooks. Transfer the meat to a platter when it is done and unwrap the garlic.
Step 5: Pour the Asian Pear Dipping Sauce into 6 small bowls, one for each diner. To eat, take a piece of meat and a grilled garlic clove (if using) and wrap them in a lettuce leaf. Dip the leaf in the dipping sauce and eat at once.