Heat the sesame oil in a large pot over medium heat, then add the sliced onions, garlic, and ginger. Cook for about 5 minutes until fragrant and soft.

Add the chuck steak pieces to the pot and sear them on all sides until browned, about 8-10 minutes.

Stir in the white miso paste, red miso (if using), light soy sauce, mirin, rice vinegar, and beef stock. Bring to a boil.

Reduce heat to low, cover, and braise the steak for about 150 minutes or until tender.

Remove the steak from the pot and let it rest for a few minutes before slicing.

Serve the sliced steak over cooked egg noodles, garnished with sesame seeds and sliced spring onion greens.