Preheat the oven to 220º C.
Place the sirloin steak on a roasting tin or baking pan. Pour over olive oil and season with ground pepper.
Roast for 15 minutes for a rare steak or 20 minutes for medium.
When it is ready to your taste, remove from the oven and allow it to cool.
Place in the refrigerator for 20 minutes to finish cooling.
If needed, turn off the oven.
While the sirloin cools down, chop the mushrooms as finely as possible. They should look like breadcrumbs. If using a food processor make sure to not liquify them.
In order to make the ‘duxelle’: add in the pan (with the mushrooms) 50g of butter and place on the heat.
Sauté the chopped mushrooms with the sprig of thyme. Cook for 10 minutes, stirring often until cooked and tender.
Season the mushrooms with salt and pepper and add the white wine. Simmer until the liquid has reduced and the mushrooms keep their shape when stirred.
Remove the ‘duxelle’ from the pan. Put aside.
Place 2 pieces of cling film on the countertop.
Extend the ham slices over the cling film overlapping slightly so that they cover the film.
On top, spread half of the ‘duxelle’, place the sirloin on top and cover with the rest of the mushroom mixture (duxelle).
With the ends of the film border cover the sirloin with the mushroom mixture. The aim is to make a parcel so that the sirloin is covered on all sides with the ‘duxelle’ like a sausage. Twist the ends as tightly as possible and place in the refrigerator while we prepare the puff pastry.
Open the puff pastry on a baking sheet.
Carefully remove the sirloin from the cling film and place on top of the pastry sheet. Make sure it is covered well with the ham and duxelle coating.
Brush the puff pastry with beaten eggs.
Cover with the other sheet of puff pastry and press it against the meat to seal any holes.
Seal the two sheets along the part where the egg was brushed using a fork or the handle of a spoon.
Brush the rest of the pastry with the rest of the beaten eggs.
With the blunt end of a knife, mark the pastry with diagonal lines making sure not to cut into it or decorate it with mixture residue, as seen in the image.
Place in the refrigerator at least for half an hour and at most for 24 hours.
Preheat the oven to 200ºC if it was turned off previously.
Brush the parcel with more beaten egg yolk and bake for 20-25 minutes until golden. If you want it slightly more well done, bake for 30 minutes.
Let it rest for 10 minutes before serving in long slices with the sauce. And finally, Enjoy!