Crafting the perfect Beef Wellington may seem daunting, but with this step-by-step guide, you will navigate through it seamlessly:

1. Prepare the Beef: Season the beef tenderloin generously with salt and black pepper. Heat olive oil in a skillet over high heat, then sear the beef on all sides until browned, about 2-3 minutes per side. Remove from heat and let it cool. Brush with Dijon mustard once cooled.

2. Mushroom Mixture: In the same skillet, add the finely chopped mushrooms and cook over medium heat until the moisture evaporates, approximately 10-15 minutes. Stir in fresh thyme and season with salt and pepper. Allow this mixture to cool.

3. Assemble: Lay out the prosciutto slices on a piece of plastic wrap, slightly overlapping. Spread the mushroom mixture evenly over the prosciutto. Place the beef in the center and roll it up tightly, using the plastic wrap for support. Chill in the fridge for at least 30 minutes.

4. Preheat Oven: Preheat your oven to 400°F (200°C).

5. Shape the Pastry: On a floured surface, roll out the puff pastry into a rectangle large enough to envelop the beef. Remove the beef from the plastic wrap and place it on the pastry.

6. Wrap the Beef: Fold the pastry over the beef, cutting off any excess pastry. Seal the edges tightly and place the Wellington seam-side down on a baking sheet.

7. Egg Wash: Brush the entire surface with beaten egg to achieve a beautiful golden finish while baking.

8. Bake: Bake in the preheated oven for 50-60 minutes, or until the pastry is golden and the internal temperature of the beef reaches 130°F (54°C) for medium-rare.

9. Rest: Once baked, remove the Beef Wellington from the oven and allow it to rest for 10-15 minutes before slicing. This step ensures the juices redistribute for a succulent bite.

10. Slice and Serve: Use a sharp knife to slice the Wellington into thick slices, revealing the luxurious filling inside.

These simple steps will guide you toward an incredible Beef Wellington that will make any occasion memorable!