Season the beef with salt and pepper and slightly sear it on each side in olive oil using a hot pan.

Brush the beef with English mustard when it comes out of the pan and leave it to rest

Put the mushrooms in the blender with the garlic, season with salt and pepper, and blend until it becomes a creme

The mushrooms need to be dried out. Cook in a dry hot pan until all the water comes out

Assemble the wellington: on a flat plastic wrap film overlap the ham slices one next to each other on two rows. The ham sheet you created has to be big enough to wrap the whole beef

Using the back of a spoon spread the mushroom paste on the ham until few inches from each edge

Lay the beef in the center and roll it using the film. now the beef is wrapped in the ham. Roll the film all around and twist the ends tight. place in the fridge to firm up for 20 minutes

Time for the final wrap: remove the film and lay the beef on the puff pastry sheet. Fold the pastry all around until the edges meet and trim off the excess. Squeeze the sizes and make sure the beef is completely enclosed in the pastry. wrap everything with plastic wrap film and twist the ends tight. Leave in the fridge for 20 min

Brush the top with egg yolk, sprinkle with salt and bake for 35-40 min at 200°C

Leave the beef to rest for at least 10 minutes after it comes out of the oven. Do not slice it to thin.