Chop the onion, the mushrooms and the parsley finely and preheat a pan on medium heat. Add the butter and sauté the onions for 2 minutes. Then add the mushrooms, season to taste with salt and pepper, add the finely chopped parsley and cook until liquid is evaporated. Take the pan from the heat and allow the stuffing to cool down.
Roll out the puff pastry, put on 4 slices of serano ham and apply the stuffing. Lay the iberico tenderloin on top, fold over the ends of the dough and roll everything up firmly.
Trim of excess dough and brush the pastry with egg wash.
Preheat your Grill on 170°C / 338°F and put the me.at on indirect heat for approximately 35-40 minutes, until desired internal temperature of the me.at is reached
Leave to rest for 5 minutes and enjoy!