Heat a pan with a little oil to a very high heat and season the pork fillets well all over. Put 1 fillet in the pan and fry for 2 mins to give it a little colour all over. Remove and repeat with the other fillet, then leave both to rest and cool.

Fry the shallot in the butter in the same pan for 2 mins, then add the mushrooms and cook until both are soft. Add the herbs and cook for 1 min. Season, tip 1/ 3 of the mixture into one bowl (reserved for the sauce) and the rest into another, and set aside to cool. Don’t wash the pan.

Meanwhile, heat a little more oil in another large pan, add the spinach and cook briefly until wilted. Set aside until cool enough to squeeze out all the excess moisture, then chop finely. Tip the spinach into the first pan and use it to wipe up all the seasoning and juices.

Overlap two pieces of cling film over a large chopping board. Lay the slices of prosciutto on the cling film in two rows, slightly overlapping. Carefully spread the pâté mixture over the prosciutto, then sit the pork fillets on top. Pack the mushrooms in the gaps, then top with the spinach. Use the cling film to draw the prosciutto around the fillet mixture, then roll it into a sausage shape, twisting the ends of cling film to tighten it as you go. Chill while you roll out the pastry.

Dust the work surface with a little flour. Roll out a third of the pastry to an 18 x 30cm strip about 2mm thick and place on a non-stick baking sheet. Roll out the remainder of the pastry to about 28 x 36cm, also 2mm thick. Unroll the fillet from the cling film and sit it in the centre of the smaller strip of pastry. Brush the pastry’s edges with the yolk mixture, as well as the top and sides of the wrapped fillet. Using a rolling pin, lift and drape the larger piece of pastry over the fillet, pressing well into the sides. Trim the joins to about a 4cm rim. Seal the rim with the edge of a spoon handle. Glaze all over with more egg yolk and, if you like, mark the wellington using the back of a knife, taking care not to cut into the pastry. Chill for at least 30 mins or up to 24 hrs.

Heat the oven to 200C/180C fan/gas 6. Brush the Wellington with a little more egg yolk and cook for 35-40 mins until golden – the pork will be just pink in the middle. Allow to stand for 10 mins before serving in thick slices.

To make the sauce, bring the cream to the boil, add the mustard and reserved mushroom mixture, and remove from the heat. Season with salt, pepper and a little lemon juice if needed and stir well before serving.