Prepare the Marinade: In a large mixing bowl, combine minced garlic, soy sauce, sake, gochujang, sesame oil, and sugar. Whisk them together until the sugar is dissolved and the ingredients are well blended.
Marinate the Beef: Add the thinly sliced beef to the bowl and ensure each piece is coated with the marinade. For the best flavor, let the beef marinate for at least 30 minutes, or for even better results, overnight in the refrigerator.
Cook the Beef: Heat a pan over medium-high heat. Once hot, add the marinated beef in batches, spreading it out to cook evenly. Sauté until the beef is fully cooked and caramelized on the edges, about 5-7 minutes per batch.
Add the Vegetables: Once all the beef is cooked, in the same pan, add the sliced onion, shredded carrot, bean sprouts, and Asian chives. Stir-fry quickly, just until the vegetables are slightly softened but still crisp.
Combine Beef and Vegetables: Return the cooked beef to the pan with the vegetables and mix well. Cook together for an additional 2-3 minutes.
Garnish and Serve: Transfer the Bulgogi to a serving dish and sprinkle with roasted sesame seeds as a garnish. Serve hot with steamed rice or wrapped in lettuce leaves.