Thinly slice the onion and king oyster mushrooms. Cut the beef into 2cm wide strips and season with salt and pepper.

Heat salad oil in a frying pan over medium heat. Sauté the onion until softened, then add the beef and cook until its color changes. Add the mushrooms and stir until well combined.

Pour in the red wine and mix. Bring to a boil, skim off any foam, cover, and simmer on low heat for 5 minutes.

Add the remaining sauce ingredients (demi-glace sauce, ketchup, Worcestershire sauce) and mix. Bring to a boil again, cover, and simmer on low heat for 7 minutes, stirring occasionally. Adjust seasoning with salt and pepper.