Prep time: 25 minutes
Cooking time: 55 minutes plus one hour chilling
Pat the fillet dry with kitchen paper, then rub all over with 1 tbsp of the vegetable oil and season well with sea salt. Heat the remaining oil in a large frying pan until smoking hot, then sear the fillet until it’s well-browned on all sides, including the ends. This should take around 8-10 minutes. Place the meat in a tray off the heat to catch any juices and remove the pan from the hob, but don’t clean it as you will use it to make the gravy. Brush the beef all over with the mustard.
Tip the watercress into a colander then pour over boiling water to wilt it, then follow with cold water to cool it down and prevent it from going brown. Squeeze the watercress to extract as much water as you can then set aside.
Lay a large piece of cling film on a work service. Lay the prosciutto on the cling film in a row, ensuring all slices overlap with no gaps. Cover the prosciutto with another layer of cling film then use a rolling pin to roll it out to a thin, even layer. Remove the top layer of cling film and scatter the wilted watercress evenly over the prosciutto, then replace the cling film and roll flat again. Remove the top layer of cling film again and sit the beef on top, then use the edge of the cling film to lift and roll the prosciutto and spinach layers to encase the beef in a tight sausage. Place the beef in the fridge for 30 minutes to firm up.
Lightly flour a clean work surface and roll the pastry to a rectangle about 8” x 10”. Lightly brush the pastry with beaten egg yolk, then carefully remove the cling film from the beef and place in the centre. Fold the shorter edges over the beef, then roll the whole piece of pastry around the fillet to encase fully. Place the Wellington in the fridge with the sealed side down and chill for at least 30 minutes or up to 24 hours.
Lightly oil a baking tray and place into an oven preheated to 200°C. Brush the Wellington with egg yolk, then use a sharp knife to gently score a criss-cross pattern all over the top. Sprinkle with sea salt then transfer to a baking tray. Roast for 10 minutes at 200°C, then turn down the over to 180°C and continue to cook for 25 minutes for rare, 30 minutes for medium rare and 35 minutes for medium. If the pastry begins to darken too much, cover with foil and continue cooking. Remove the Wellington from the oven and leave to rest for a minimum of 15 minutes.
Next, make the gravy by heating the butter in the pan used to sear the beef. Fry the shallot, thyme and bay leaf, using a wooden spoon to incorporate the bits of caramelised beef on the bottom of the pan. Scatter over the flour and continue to fry until golden brown, then add the red wine and reduce to a thick paste. Add the beef stock cube and 250ml of boiling water along with the resting juices from the beef and simmer for five minutes. Pass the gravy through a sieve into a jug and season to taste.
Cut the Wellington into six generous slices and serve with the gravy on the side.
800g beef fillet
2 tbsp vegetable oil
12 slices smoked prosciutto
500g ready-made puff pastry
2 egg yolks
1 tbsp English mustard
For the gravy:
1 shallot, finely sliced
1 sprig thyme
1 bay leaf
1 tbsp plain flour
1 knob butter
1 large glass red wine
1 beef stock cube