• Puree onion-garlic-ginger-pear. In a food processor, combine 1/2 onion cut into chunks, pear chunks, garlic, and ginger. Whizz until pureed. You may have to scrape the bowl down several times during the process. (Or, grate with a box grater until juicy.) Scrape into a large bowl. 
• Combine marinade together. In a large bowl, add onion-garlic-ginger-pear puree. Add 1/2 onion (thinly sliced), green onions, soy sauce, sugar, Mirin or rice wine, sesame seed oil, black pepper, and sesame seeds. Mix with a spoon until combined. 
• Add thinly sliced beef. Add beef and mix well until it's coated completely with the marinade. Rest at room temperature for 15 minutes. 

To cook:

• Non-stick skillet: heat over medium heat. Add 1 Tbsp neutral oil and add the bulgogi in one layer. Spread around with chopsticks and leave undisturbed for that bbq char, about 2-3 minutes. When the edges look cooked and the juices begin to release, mix around with a cooking spoon until the meat is no longer pink and cooked through. Continue cooking until the sauce has reduced somewhat and the meat is dark brown and caramelized.
• Cast iron skillet: heat over medium high heat. When the cast iron is hot, add 1 Tbsp neutral oil and swirl around in the pan. The oil should be smoking. Add bulgogi in one layer. Leave the meat undisturbed, to get that bbq char on one side. When the bulgogi looks brown and crispy on the edges, mix around with a metal spatula and finish cooking. The meat will release a lot of juice. The cooking process should take 5-8 minutes total!
• Wok: heat over high heat. Add 1 Tbsp neutral oil and swirl around. Add the bulgogi in one layer. Spread around with chopsticks and leave undisturbed for that bbq char, about 2-3 minutes. When the edges look cooked and the juices begin to release, mix around with a cooking spoon or metal spatula until the meat is no longer pink and cooked through, tossing as you go. Continue cooking until the sauce has reduced somewhat and the meat is dark brown and caramelized.
• Sheet pan: Adjust the oven rack so the top rack is 5-6 inches from the heat source at the top. Turn the oven to broil function and let it preheat for 10 minutes. Line a sheet pan with foil for easy clean up. Spread out bulgogi in an even layer, making sure it's not too crowded. When the oven has fully preheated, broil until fully cooked with crispy edges, about 6-8 minutes.

To serve:

• Serve. Transfer to a platter, making sure to include all the juices. Garnish with additional green onion and sesame seeds. Serve with lettuce wraps, rice, and kimchi for a complete meal. Ssam sauce is also a nice addition.