Method

• 1.
  Preheat the oven to 200°C. Heat 2 tablespoons oil in a frypan over medium-high heat. Season the beef, then cook, turning, for 4-5 minutes until sealed on all sides. Transfer to a roasting pan and scatter with thyme. Roast for 15 minutes for rare. Rest, loosely covered with foil, for 10 minutes.
• 2.
  Meanwhile, heat remaining 2 tablespoons oil in a frypan over high heat. Add onion rings and cook for 2-3 minutes until golden. Turn, season, then reduce the heat to low. Cover and cook onion rings for a further 10 minutes until just tender. Remove from the heat, then stand, covered, for 10 minutes.
• 3.
  If using, grate 1 teaspoon fresh truffle, into the mayonnaise, stirring to combine. Alternatively, replace the fresh truffle with 2 teaspoons truffle oil. Set aside.

• 4.
  Thickly slice the beef and arrange on a platter. Brush the beef slices with 1 1/2 teaspoons truffle oil, then shave remaining fresh truffle using a vegetable peeler or mandoline and scatter over the beef with the micro herbs. Drizzle beef with remaining 1 1/2 teaspoons truffle oil, then serve with the onion rings, watercress and truffle mayonnaise.