Prepare the broth and tenderloin. Place the shank in cold water. Bring to a boil, skimming off any foam. Then add the whole onion and whole ginger. Simmer for 3 hours. Sprinkle the sliced beef tenderloin in a separate bowl with salt and pepper. Leave for 15 minutes. Increase the heat 5 minutes before the broth is ready. The liquid should literally boil in the pan. Lower the beef tenderloin into the boiling broth using a slotted spoon for 2-3 seconds. Then put the meat back in a separate bowl.
Prepare the noodles. Place them in cold water and bring to a boil. Cook for 3 minutes. Then drain in a colander.
In each bowl, first put the noodles, then the onion rings, chopped ginger, meat, hot pepper. Pour in the broth. Add a slice of lemon, herbs and 2 tbsp. soy sauce.