Beef

Pulse the mushrooms to a rough paste in a food processor, cook the paste in a pan over high heat until moisture evaporates, then spread to cool
Heat a frying pan with olive oil, season and sear the beef for 30 seconds per side, then remove and cool
Brush the cooled beef all over with English mustard
Lay cling film on a work surface, arrange Parma ham in overlapping rows, spread the mushroom paste over the ham, place the seared beef in the centre, roll tightly, twist the cling film ends to secure and chill 15–20 minutes
Roll out the puff pastry on a floured surface to a large rectangle about the thickness of a £1 coin
Remove the cling film from the beef, place the beef in the centre of the pastry, brush the surrounding pastry with beaten egg yolk, fold and wrap the pastry around the beef, trim excess, turn the seam underneath, brush all pastry with egg and chill 15 minutes
Preheat the oven to 400°F.
Score the pastry at 1cm intervals, glaze with beaten egg yolk, bake at 400°F for 20 minutes, then reduce to 350°F and bake for a further 15 minutes.
Allow the Wellington to rest for 10–15 minutes before slicing and serving