Put the mushrooms into a food processor with some seasoning and pulse to a rough paste. Scrape the paste into a pan and cook over high heat for about 10 minutes, tossing frequently, to cook out the moisture from the mushrooms. Spread out on a plate to cool.

Heat in a frying pan and add the olive oil. Season the beef with salt and pepper all over then sear in the hot pan for 30 secs only on each side. (You don't want to cook it at this stage, just colour it). Remove the beef from the pan and leave to cool, then brush all over with the mustard.

Lay a sheet of cling film on a work surface and arrange the Parma ham slices on it, in slightly overlapping rows. With a palette knife, spread the mushroom paste over the ham, then place the seared beef fillet in the middle.

Keeping a tight hold of the cling film from the edge, neatly roll the Parma ham and mushrooms around the beef to form a tight barrel shape. Twist the ends of the cling film to secure. Chill for 15-20 minutes to allow the beef to set and keep its shape.

Roll out the puff pastry on a floured surface to a large rectangle, the thickness of a £1 coin. Remove the cling film from the beef, then lay it in the centre. Brush the surrounding pastry with egg yolk.

Fold the ends over, then wrap the pastry around the beef, cutting off any excess. Turn over, so the seam is underneath, and place on a baking sheet. Brush over all the pastry with egg and chill for about 15 minutes to let the pastry rest.

Heat the oven to 200C (180C, Gas 6). Lightly score the pastry at 1cm intervals and glaze again with beaten egg yolk. Bake for 20 minutes, then lower the oven setting to 180C (160C fan, Gas 4) and cook for another 15 minutes.

Allow resting for 10-15 minutes before slicing and serving with the side dishes of your choice. The beef should still be pink in the centre when you serve it.