Pat the 2 kg beef tenderloin dry and season it all over with the salt and black pepper.

Heat 1 tablespoon of extra virgin olive oil in the frying pan over high heat. Sear the beef tenderloin on every side until browned, about 1 to 2 minutes per side.

Remove the seared beef tenderloin from the frying pan and brush it all over with the mustard. Set it aside to cool completely.

Finely chop the 150 g champignon mushrooms. Melt the butter in the frying pan over medium heat.

Cook the chopped champignon mushrooms in the butter until their moisture has evaporated and they form a dry mushroom paste. Season with a little salt and black pepper.

Lay the 300 g prosciutto crudo in overlapping slices on plastic wrap. Spread the cooled mushroom paste evenly over the prosciutto.

Place the mustard-coated beef tenderloin on the mushroom-covered prosciutto. Roll the prosciutto tightly around the beef using the plastic wrap.

Refrigerate the wrapped beef tenderloin for 15 minutes so it firms up. Preheat the oven to 200 to 220°C.

Unroll the 3 puff pastry sheets and overlap them to create a pastry sheet large enough to enclose the beef. Place the chilled wrapped beef in the center.

Wrap the puff pastry tightly around the beef and seal the seams. Place the parcel seam-side down on the baking tray.

Bake the Beef Wellington at 200 to 220°C for 30 minutes. Check that the center reaches about 52 to 55°C for medium-rare beef.

Rest the baked Beef Wellington for 10 minutes before slicing. Serve while the pastry is hot and crisp.