Cut beef into thin slices (thinly sliced meat that you can almost see through)
In a bowl, combine 6 tablespoons soy sauce and 2 tablespoons sugar (optional: 3 tablespoons gochujang), mix well until sugar dissolves.
Add 1 tablespoon sesame oil to the base sauce
In a blender, combine ⅓ cup onion, ⅓ cup Korean pear, ⅓ cup water, and 0.5 tablespoon garlic, blend until smooth
Mix the blended mixture with the base sauce
Add 3 tablespoons mirin or sake, 0.5 tablespoon oyster sauce, and black pepper to taste
Place sliced beef in the marinade and mix well, ensuring all meat is coated
Marinate for at least 30 minutes (preferably 24 hours) in the refrigerator
Heat oil in a pan over medium to low heat
Cook the marinated beef until about 70-80% done
Add the chopped onion and scallions to the pan
Continue cooking until meat is fully cooked
Garnish with sesame seeds before serving
Serve with lettuce, samjang, rice, and radish
