Prep Time: 45 min (plus chilling) Cook Time: 25–35 min Total Time: ~2.5 hr (including chilling)
Sear Beef:
Season tenderloin with salt and pepper. Sear on high heat until browned (2–3 min per side). Brush with mustard, cool.
Make Duxelles:
Pulse mushrooms, shallots, and garlic until finely chopped. Cook in a dry non-stick pan over medium heat until dry (10 min). Add bourbon, cook until evaporated (10 min). Season, cool.
Assemble:
Lay plastic wrap on a damp board. Arrange prosciutto in a rectangle, spread with duxelles. Place beef on top, roll tightly using plastic. Chill 1 hr.
Wrap:
Roll out puff pastry on a floured surface. Unwrap beef, place at pastry bottom, roll tightly, seal edges. Brush with egg wash. (Optional: Add lattice-cut pastry on top.) Chill 30 min.
Bake:
Preheat oven to 175°C (350°F). Bake 20–25 min for medium rare (52–54°C/125–130°F) or 30–35 min for medium (57–60°C/135–140°F). Rest 10 min.
Serve:
Slice with a serrated knife. Serve with sides.