Meanwhile, place a large frying pan over a high heat.
Mix half the Sriracha seasoning with the oil and then rub on the steaks.
Sear the steaks until charred but still rare (2 minutes per side), then transfer to a plate.
In a large pan add the onion, ginger, beef stock, star anise, the rest of the Sriracha seasoning and the cinnamon sticks. Bring to the boil then reduce the heat and simmer for about 20 minutes.
Meanwhile drain the noodles and thinly slice the steak.
Add the fish sauce to the broth and boil for 5 minutes, then strain to discard the onion, ginger and spices. Add the bean sprouts to the broth.
Divide the noodles among 10 bowls, then top with the broth, beef, spring onions and coriander.
