Ingredients:

2 pounds beef 5-bone chuck flanken
1/2 cup soy sauce
1/4 cup brown sugar
4 cloves garlic, minced
2 tablespoons sesame oil
2 tablespoons rice vinegar
1 tablespoon gochujang (Korean chili paste)
1 teaspoon black pepper
1 onion, sliced
4 green onions, sliced
1/4 cup toasted sesame seeds
Vegetable oil, for cooking
Cooked rice, for serving

Instructions:

In a bowl, mix together the soy sauce, brown sugar, minced garlic, sesame oil, rice vinegar, gochujang, and black pepper.
Add the beef 5-bone chuck flanken to the marinade and mix well to coat.
Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or overnight for best results.
Heat some vegetable oil in a large skillet or wok over high heat.
Add the sliced onion to the skillet and stir-fry for 1-2 minutes until it starts to soften.
Add the marinated beef 5-bone chuck flanken to the skillet and stir-fry for 4-5 minutes until browned and cooked through.
Add the sliced green onions and toasted sesame seeds to the skillet and stir-fry for another minute.
Serve the Korean-style Beef 5-Bone Chuck Flanken with cooked rice on the side.
Enjoy your delicious and flavorful dish!