Beef Wellington with mushrooms

Ingredients:

• One piece (900 g) of beef tenderloin, tied with twine
• 1 sheet frozen puff pastry (250g), thawed
• Coarse salt and ground black pepper
• 3 tbsp. l. olive oil
• 450 g mushroom caps
• 4 tbsp (60 g) butter
• 1 shallot, chopped
• 2 tbsp. heavy cream
• 2 tbsp. breadcrumbs
• 2 tbsp finely chopped fresh parsley
• 2 tbsp mustard
• 1.5 tbsp. horseradish
• 1 large egg
• Flour for rolling out the dough
• Flaky sea salt for sprinkling

Preparation:

1. Season the tenderloin generously on all sides with salt and pepper. Heat 2 tablespoons of oil in a large skillet over high heat. Brown the beef on all sides for 8 to 10 minutes. Transfer to a baking sheet and cool completely, about 20 minutes.
2. Add half the mushrooms to a food processor and process until very finely chopped. Transfer the finely chopped mushrooms to a bowl and repeat with the other half.
3. In a large skillet, heat the butter and 1 tablespoon of the remaining oil over medium-high heat. When the butter begins to shimmer, add the shallots and cook until softened, about 4 minutes. Add the mushrooms to the skillet and cook until all the moisture has evaporated, about 10 minutes.
   
   Add the heavy cream and simmer until thickened, about 2 minutes. Turn off the heat and stir in the breadcrumbs and parsley. Transfer the mushrooms to a small bowl, cool completely, and refrigerate for at least 1 hour. After this time, the mushroom mixture will resemble a paste.
4. Combine the mustard and horseradish in a small bowl. Once the meat has cooled, cut off the string and discard it, then spread the mustard mixture over the beef. Refrigerate and chill for 1 hour.
5. Place a rack in the center of the oven and preheat to 200°C. Line a baking sheet with parchment paper.
6. Beat the egg in a small bowl. Dust the work surface with flour. Roll out the puff pastry with a rolling pin until it's 10 cm longer than the tenderloin and 15-17 cm wider. Brush the edge of the pastry with beaten egg. Spread the mushroom mixture over the entire surface and sides of the beef.
   
   Place the beef, mushroom side down, in the center of the dough and spread the remaining mushroom paste over it. Fold the two ends of the dough over the end of the beef and then roll it up.
   
   Place the roll seam-side down on a baking sheet. Brush the surface of the dough with egg wash. Make 3 slits in the top of the roll and sprinkle lightly with flaky sea salt.
7. Roast the beef Wellington until a thermometer inserted into the meat registers 120°F (50°C), about 40 minutes.
   
   Remove from the oven and let rest for 20 minutes before slicing into 2.5cm thick slices. The internal temperature of the meat will rise to 125°F (52°C), and the beef should be medium-rare with a beautiful ruby-red color.