Follow these steps to prepare a traditional Beef Wellington featuring a perfectly cooked beef tenderloin wrapped in duxelles, prosciutto, and puff pastry.
Season the beef tenderloin generously with salt and pepper. Sear all sides in hot olive oil until browned, about 1-2 minutes per side. Remove from heat and brush all over with Dijon mustard. Chill the beef for at least 20 minutes.
Prepare the duxelles: Pulse mushrooms, shallots, and garlic in a food processor until finely chopped but not pureed. Cook the mixture in a dry skillet over medium heat, stirring often, until all moisture has evaporated (about 15-20 minutes). Stir in white wine and thyme; cook until the wine evaporates. Season and spread the duxelles mixture onto a plate to cool completely.
Lay a large sheet of plastic wrap on your work surface. Arrange the prosciutto slices in an overlapping rectangle large enough to wrap the tenderloin. Spread the cooled duxelles evenly over the prosciutto.
Place the chilled tenderloin at one end of the prosciutto. Use the plastic wrap to tightly roll the prosciutto and duxelles around the beef. Twist the ends of the plastic wrap to secure a tight cylinder. Chill for 30 minutes to firm up.
Roll out the puff pastry on a lightly floured surface into a rectangle large enough to encase the beef. Remove the plastic wrap from the beef and place the beef seam-side down on the pastry. Brush the edges of the pastry with the beaten egg.
Fold the pastry over the beef, trimming any excess. Crimp the edges firmly to seal completely. Wrap tightly in plastic wrap again and chill for at least 30 minutes, or up to 24 hours.
Preheat your oven to 400°F (200°C). Brush the chilled Wellington all over with the egg wash. Score the top lightly with a knife in a decorative pattern, avoiding cutting through to the meat.
Bake for 30-40 minutes, or until the pastry is golden brown and the internal temperature reaches 125°F (52°C) for medium-rare.
While the Wellington bakes, make the sauce: Simmer red wine in a small saucepan until reduced by half. Add beef broth and reduce again until slightly thickened. Whisk in the cold butter off the heat. Season.
Let the Beef Wellington rest for 10-15 minutes before slicing thickly and serving with the red wine sauce.
Notes
Chilling the components at each stage helps maintain the shape and prevents a soggy bottom crust.
Use a meat thermometer inserted through the pastry into the center of the beef for accurate cooking.
For an extra crisp crust, place the pastry-wrapped Wellington in the freezer for 15 minutes before the final egg wash and baking.