Preheat your oven to 400°F (200°C).

Season the beef tenderloin with salt and pepper, then sear it in a hot pan for 2-3 minutes on all sides until it’s beautifully browned. Let it cool to room temperature afterward.

Sauté the cremini mushrooms in the same pan, cooking until all the moisture evaporates and they turn golden brown. Add the fresh thyme.

Layer prosciutto slices on plastic wrap, spread mushroom mixture over, place cooled beef on top, and roll tightly.

Roll out the puff pastry on a lightly floured surface, wrap it around the beef log tightly, and seal the edges.

Brush the pastry with the beaten egg and bake for 25-30 minutes until golden and crispy.