Season the steaks with freshly crushed black pepper. Spread pancetta with mustard and roll tightly around the steak, secure with a string or foil. Remove the mushroom stems and chop, cook with the garlic and cream, allow cooling. Add grated cheese and stuff into to the mushroom cups, place on a baking tray and cook in a hot oven for 5 minutes. Peel and slice the onions into 1 cm discs, drizzle with balsamic vinegar, olive oil and herbs, bake in a hot oven until soft. Peel the potatoes and cut the potatoes thickly and deep fry until soft but not browned. Allow the oil to go higher in temperature and deep fry again, remove from the oil. Go higher with the temperature and deep fry the third time. Season with salt and drizzle with the truffle oil. Grill the steak to your liking, serve, top up with the onions and mushrooms, drizzle with the beef jus. Serve the chips on the side.