Heat the sesame oil in a large pot over high heat. Add the cut beef brisket and season with salt and pepper. Cook until browned on all sides, for about 3-4 minutes.
Mix the garlic, red pepper powder, soy sauce and red pepper paste in a bowl and add to the pot. Add the royal fern, onions and beef broth. Bring to a boil and cover the pot and simmer on low until the meat is tender, about 40 minutes.
In a separate pot, just a few minutes before the 40 minutes is up, boil some water and cook the noodles. You only need to boil these noodles for about 3-4 minutes.
To the beef soup, add the bean sprouts, noodles, green onions and tofu (if using). Cook for about 10 minutes. Serve and add fresh diced green onion garnish to each bowl.