Preheat the oven to 200C/400F/Gas 6.
For the beef with cashew crust, rub the beef all over with olive oil and season well with salt and freshly ground black pepper.
Heat an ovenproof frying pan until hot and fry the beef for 2 minutes on each side. Spread the mustard over the top of the beef.
Place the breadcrumbs, cashew nuts and parsley into a bowl and mix well. Press this mixture onto the mustard-covered beef, then transfer to the oven and bake for five minutes, or until the crust is golden-brown and the beef is cooked to your liking.
For the wild mushroom sauce, heat the butter and oil in a frying pan and gently fry the onion, ginger and garlic until softened but not coloured.
Add the wild mushrooms and soy sauce and cook until the mushrooms have softened. Add the cream, season, to taste, with salt and freshly ground black pepper and stir well.
To serve, place the beef onto a plate and drizzle over the sauce.