Fry the onion, garlic, carrots, and celery in 30ml of oil until golden-brown and place in a casserole dish.
Cut a deep pocket into the side of the beef fillet, leaving 2cm gaps at the ends.
Stuff the pocket with 1.5cm pâté strips, drizzle with truffle oil, and season the meat.
Wrap the beef in bacon, securing with kitchen string and tucking in bay leaves.
Preheat the oven to 180°C.
Brown the wrapped beef in the frying pan for 12 minutes before placing it over the vegetables.
Whisk flour into the pan fat, then stir in cognac, Madeira, and beef stock to create a sauce.
Pour sauce around the beef and roast at 180°C for 30 to 40 minutes depending on desired doneness.
Rest the meat under foil, thicken the sauce on the hob, and strain through a sieve.
Carve the beef into thick slices and serve with the strained sauce and parsley garnish.