Preheat your oven to 400°F (200°C).
Season the pork tenderloin with salt and pepper. Brush the tenderloin with maple syrup for a sweet glaze. In a skillet, heat olive oil over medium-high heat. Sear the pork on all sides until browned, about 2 minutes per side. Remove from heat and let it cool.
Make the Mushroom Duxelles: In the same skillet, melt the butter over medium heat. Add chopped chestnut mushrooms, shallots, garlic, and rosemary. Cook until the mushrooms are golden brown and the shallots are translucent, about 7-8 minutes. Pour in the dry sherry and cook until the liquid has evaporated. Remove from heat and let it cool slightly.
On a clean surface, lay out the slices of prosciutto overlapping slightly to form a rectangle. Spread the mushroom duxelles evenly over the prosciutto. Place the seared pork tenderloin in the center. Carefully roll the prosciutto and mushrooms around the pork to form a tight cylinder.
Roll out the puff pastry sheet on a lightly floured surface. Place the prosciutto-wrapped pork in the center and fold the pastry over, sealing the edges. Trim any excess pastry if needed. Place the Wellington seam side down on a baking sheet lined with parchment paper.
Brush the top of the pastry with the beaten egg for a glossy finish. Use a knife to score the top of the pastry lightly. Bake in the preheated oven for 25-30 minutes or until the pastry is golden brown and the pork reaches an internal temperature of 145°F (63°C) for medium doneness.
Let the Pork Wellington rest for 5-10 minutes before slicing. Serve with a side of cranberry compote and roasted Brussels sprouts for a festive touch.
