To make Wellington beef first of all salt and pepper the whole fillet.

Heat some oil in a pan and sear the meat on all sides to seal it. (this process will ensure that all the meat juices stay inside the fillet)

Put the sealed fillet on a dish and brush it with mustard while it is still hot.

In a food processor mince the champignon mushrooms with a pinch of salt and the garlic clove.

Pour the chopped mushrooms in a pan and heat them to let the vegetation water evaporate. Add some fresh thyme and let cool completely.

When all the ingredients come to room temperature you can assemble the Wellington beef.

First of all line a chopping board with plastic wrap, cover it with the slices of Prosciutto di San Daniele making an even layer with the slices slightly overlapping.

Spread on the prosciutto the mushroom mix and level it with a spoon.

Sit the fillet on the mushroom layer and wrap it up like a jelly roll. Press it down gently with your hands until it is well sealed.

Wrap it all up firmly in the plastic wrap to give it a nice cylindrical shape and chill it in the fridge for 15 minutes.

In the meantime line again the chopping board with plastic wrap and roll out the puff pastry on it.

After 15 minutes take the fillet out of the fridge and unravel it from the plastic wrap.

Sit the fillet on the puff pastry and roll it in, allowing a few centimeters of pastry to overlap.

Get rid of the excess pastry and press well to seal the fillet properly in the pastry casing.

Wrap it all up again in plastic wrap to give it a perfect shape and chill it in the fridge for 15 more minutes.

Put the Wellington beef, without the cling film, on a baking tray lined with baking paper.

Beat the egg yolks with 1 teaspoon of water and brush the top and the edges of the pastry.

Decorate the surface using the back of a knife to mark it with long diagonal lines, taking care not to cut into the pastry, then sprinkle lightly with salt.

Bake it in a 200°C oven for 30-40 minutes. (the cooking time depends from the thickness of the fillet, but it should be medium-rare in the middle).

Take it out of the oven and let it sit for at least 10 minutes before slicing it.

Slice and serve the Wellington beef with baked sweet potatoes.