Substitute fillet with sirloin, ribeye or rump steak.
For the mustard mushroom sauce, heat the butter in a small saucepan over a medium-high heat and sauté the onion until soft and translucent.
Reduce the heat to medium. Add the mushrooms and garlic and sauté for about 5 minutes until the mushrooms are reduced but still plump.
Whilst you’re waiting, prepare the beef fillet by cutting away the silver skin. Carefully slide the tip of a sharp knife under the membrane and move the knife along it at an upward angle pulling the silver skin off of the meat.
Stir the cream and two mustards into the mushroom sauce, turn the heat down to low and let simmer until thickened, about 5 minutes. Season well with salt and freshly ground black pepper and add the truffle oil (optional).
Slice off the tail end of the fillet (keep this as a chef’s snack) and portion into 4 even pieces.
Tie butcher’s string around each medallion to help keep their shape during cooking.
Coat the fillet steaks in olive oil and generously season with salt and freshly ground black pepper.
Add a splash of olive oil and a knob of butter to a smoking hot frying pan and cook the filet mignon for approximately 6 to 8 minutes (2 minutes per side - top, bottom and sides) for medium-rare.
To evenly brown all sides of the fillet, continuously spoon the hot butter from the pan over the steaks whilst cooking; this French technique is called arroser which means ‘to baste’.
Leave the meat to rest for half its cooking time before spooning creamy mustard mushroom sauce over the fillet medallions and garnishing with chopped parsley. Just about any side dish will accompany this mouth-watering meal.