Prepare the Beef: Lay the tenderloin on a large cutting board. To butterfly it, make a lengthwise cut down the centre, stopping about 2 cm from cutting all the way through. Open the fillet like a book. Cover with cling film and gently pound with a meat mallet or rolling pin to an even thickness of about 2-3 cm. This technique creates a large, flat surface for the filling. For a great visual guide, you can check out this explanation on butterflying meat. Remove the cling film and season the inside generously with salt and pepper.

Cook the Stuffing Base: Place a large, heavy-bottomed frying pan over a medium heat. Add the diced pancetta and cook for 5-7 minutes, until it's crispy and the fat has rendered. Remove the pancetta with a slotted spoon and set aside, leaving the rendered fat in the pan.

Sauté the Aromatics: Add the chopped shallots to the pan and cook for 3-4 minutes until softened. Add the minced garlic and cook for another minute until fragrant. Add the finely chopped mushrooms, season with a pinch of salt and pepper, and cook for 10-12 minutes, stirring occasionally, until all the liquid has evaporated and the mushrooms are deeply browned. This step is key to developing a rich, umami flavour.

Combine the Stuffing: Scrape the mushroom mixture into a large mixing bowl and allow it to cool completely for at least 20 minutes. Once cooled, add the cooked pancetta, toasted pine nuts, breadcrumbs, grated Parmesan, chopped parsley, and the beaten egg. Mix everything together until well combined.

Stuff and Roll the Tenderloin: Spread the stuffing mixture evenly over the surface of the butterflied beef, leaving a 2 cm border around the edges. Starting from one of the long sides, tightly roll the beef up into a log.

Tie the Roast: Secure the roast using butcher's twine. Tie pieces of twine at 3-4 cm intervals along the length of the tenderloin to ensure it holds its shape while cooking. I find that starting in the middle and working my way out helps create the most uniform shape.

Sear the Beef: Pat the outside of the beef dry with paper towels and season generously all over with salt and pepper. Heat the olive oil and butter in your large frying pan over a medium-high heat. Once the pan is very hot, carefully place the tenderloin in the pan and sear for 2-3 minutes per side, until a deep golden-brown crust has formed all over.

Roast to Perfection: Preheat your oven to 200°C (180°C fan). Transfer the seared tenderloin to a roasting tin and place it in the preheated oven. Roast for 20-25 minutes for medium-rare. The most accurate way to check for doneness is with a meat thermometer inserted into the thickest part of the meat – it should read 52-54°C for medium-rare.

Rest the Meat: This is a crucial step! Transfer the roasted tenderloin to a clean cutting board, tent loosely with foil, and let it rest for 15 minutes before slicing. This allows the juices to redistribute throughout the meat, ensuring every slice is moist and tender.

Serve: Remove the twine, slice the tenderloin into thick rounds, and arrange on a platter to serve immediately.