Begin by coring and peeling the Fuji apple. Cut it into chunks and place it in a blender or food processor. Add the garlic cloves, soy sauce, light brown sugar, granulated sugar, water, sesame oil, and plum extract (if using). Blend until you achieve a smooth consistency.
In a large mixing bowl, combine the thinly sliced ribeye steak with the marinade. Make sure each piece of meat is well-coated. You can also use a plastic zip-top bag for easy mixing and marinating. Seal it well and refrigerate for at least 30 minutes, or up to overnight for deeper flavor.
While the beef is marinating, peel and thinly slice the yellow onion. In a skillet over medium heat, add a drizzle of sesame oil and sauté the onions until they are soft and translucent. This step enhances their sweetness and adds depth to the dish.
Once the beef has marinated, remove it from the fridge. In the same skillet with the sautéed onions, increase the heat to high. Add the marinated beef, allowing it to sear and caramelize for about 5 to 7 minutes, stirring occasionally. The beef should be cooked through and slightly charred for that delicious flavor.
Transfer the cooked beef bulgogi to a serving platter. You can garnish it with sesame seeds or sliced green onions if desired. Serve it hot with steamed rice, lettuce wraps, or alongside your favorite side dishes. Enjoy the explosion of flavors in every bite!