First Step: Prepare the Beef Trim the beef tenderloin of any excess fat or silver skin. Lightly season with salt and pepper to enhance its natural flavors. Allow the beef to come to room temperature to promote even cooking.

Second Step: Sear the Beef In a hot skillet, sear the beef tenderloin on all sides for about 2-3 minutes each to develop a flavorful crust. Remove from heat and let it cool completely. This step locks in juices and adds rich flavor.

Third Step: Make the Mushroom Duxelles Finely chop the cremini mushrooms and sauté them in a dry pan over medium-high heat. Stir frequently to release moisture, cooking until the liquid evaporates and the mixture thickens, about 10-12 minutes. Season with salt, pepper, and thyme to taste.

Fourth Step: Assemble the Wellington Brush the cooled beef with Dijon mustard evenly. Lay out prosciutto slices on plastic wrap, spread the mushroom duxelles over the prosciutto, then place the beef on top. Using the plastic wrap, carefully roll the prosciutto and duxelles around the beef to form a tight barrel shape. Chill this wrapped beef in the refrigerator to firm up the shape.

Fifth Step: Wrap with Puff Pastry Roll out the puff pastry on a floured surface large enough to envelop the beef. Remove the plastic wrap from the beef roll and place it onto the pastry. Fold the pastry around the beef, sealing the edges well. Trim and decorate pastry edges if desired. Brush the pastry with the beaten egg wash to help it bake to a golden brown.

Final Step: Bake the Wellington Place the wrapped beef on a baking tray lined with parchment paper. Bake in a preheated oven at 400°F (200°C) for 25-30 minutes or until the pastry is golden and crisp and the beef reaches your desired internal temperature (125°F for medium-rare). Let the Wellington rest for 10-15 minutes before slicing to retain juices and serve.