Spread a duxelle (yeah, ok, chopped mushrooms) on to some serrano ham laid out on baking parchment, put the beef fillet on and wrap it up.
Cook it for what feels like not enough time; hold your nerve and you’re in.
Method
Make the duxelle: put a little oil and butter in a pan and heat until the butter is foaming. Add chopped shallot and whatever herbs you’re using and soften the shallot, then add the chopped mushrooms and cook until it is fairly dry. Leave it aside to cool
Put a little fat in a frying pan; animal fat I sideal but don’t worry too much, veg oil is fine.
Season the meat and brown it all over; don’t cook it, youre just trying to seal in all that lovely juiciness.
Lay enough prosciutto on baking paper or cling film for the beef to be completely wrapped in.
Spread the duxells is a wide stripe across the middle of the prosciutto (so it’s on top when you roast the meat).
Wrap it up tightly and put it on a baking tray with the joins in the ham on the bottom.
Drizzle with a small amount of olive oil and roast in a hot oven (200+) for 20 minutes then turn it down to 180 for the rest of the cooking time.