Trim off the fat from beef and slice thinly across grain. Spread the beef slices around cutting board. Place cutting board on sturdy counter top. Smack them with knife in different directions. Turn over to the other sides and continue to chop the meat until you see them into small irregular chunks.
Place beef in a bowl and add pear and onion puree. Mix them well. Set aside for 10 minutes.
Add nuts, Asian leek, garlic, soy sauce, sugar, sesame oil, sesame seeds, and pepper to beef in a bowl.
Mix them thoroughly by squeezing or kneading them many times so the beef can soak up the marinade, about 5 minutes. Cover with plastic wrap and let it chill for at least 1 hr.
Heat your grill or grill pan over medium high heat. Spray with some oil. Scoop up the beef mixture with spoon and place it on the pan, flattening with your fingers, about 1/4" thick. Sear for 2 minutes and turn over to the other side. Continue to cook for another 1-2 minutes until you see the nice grill marks.
Before serving baste with the basting sauce to add shine and more flavor to the meat.
Serve immediately with some lettuce and Korean chili paste (gochujang) or ssamgjang.