Prepare Beef (Time: 0-40 minutes):
Partially freeze 600g beef sirloin or ribeye for 30-40 minutes until firm but not solid.
Slice against grain into paper-thin slices (?-inch thick). Place in large bowl.
Make Marinade (Time: 40-50 minutes):
Blend 1/2 Asian pear (peeled, cored), 1/2 onion, 5 garlic cloves, 1-inch ginger until completely smooth.
In bowl, combine pear puree with 1/2 cup soy sauce, 3 tbsp sugar, 2 tbsp sesame oil, 1 tsp black pepper. Whisk until sugar dissolves.
Marinate (Time: 50 minutes + 2 hours):
Pour marinade over beef. Mix thoroughly with hands until all slices are coated.
Cover, refrigerate minimum 2 hours, preferably overnight (up to 24 hours).
Cook (Time: 2 hours 0-15 minutes):
Heat large skillet, grill pan, or outdoor grill to high heat.
Cook in batches without overcrowding: 2-3 minutes per side until caramelized and cooked through.
Do not overcook or beef will become tough.
Garnish and Serve (Time: 2 hours 15-20 minutes):
Sprinkle with 1 tbsp toasted sesame seeds and chopped scallions.
Serve immediately with steamed rice, lettuce leaves (for wrapping), and side dishes.