Soak flat rice noodles in plenty of water for 20 minutes. Peel and roughly chop the ginger. Peel the onion and halve it. Cook the ginger and onion in a saucepan over medium heat for two minutes, stirring.
Add a pinch of sugar and deglaze with the beef broth. Let simmer for 10 minutes. Cut spring onions into fine rolls. Finely chop the coriander and mint.
Pour the broth through a fine sieve into a second pot. Season with the juice of half a lime and soy sauce. Drain the flat rice noodles and cook in the broth for two to three minutes. Divide spring onions, sprouts and herbs INTO TWO bowls. Top up with broth and noodles. Finally, slice the meat as thinly as possible, SALT it and add it to the soup.