Beef Wellington Tenderloin

Ingredients:

• 900 g mixed mushrooms (e.g. cremini, button, shiitake and/or oyster mushrooms), trimmed and cut into pieces or torn
• 60 g unsalted butter
• 2 shallots, finely chopped
• 2 tsp fresh thyme, chopped
• 1/4 cup cognac or brandy
• 1 center cut of beef tenderloin (1 - 1.2 kg), trimmed and trussed at 2.5 cm intervals.
• 1 tbsp. vegetable oil
• 110 g thin slices of prosciutto
• 2 tablespoons Dijon mustard
• 1 large or 2 small sheets of frozen puff pastry (400-500g total), thawed
• Premium flour, for dusting
• 1 large egg, lightly beaten
• Sea salt flakes
• Chopped chives, for serving

Preparation:

1. Pulse the mushrooms in two batches in a food processor until finely chopped, 10-15 pulses. Heat 3 tablespoons butter in a large skillet over medium-high heat. Add the shallots and thyme and cook until softened, 1-2 minutes.
2. Add the mushrooms and cook, stirring frequently, until they are dry and begin to crumble into fine crumbs, 25 to 28 minutes.
3. Remove the pan from the heat and add the cognac. Carefully return the pan to the heat (the cognac may ignite) and continue cooking until the mushroom mixture is dry and the alcohol has evaporated, 2-3 minutes. Add the remaining 1 tablespoon of butter and season with coarse salt and black pepper. Remove from the heat and let cool completely.
4. Meanwhile, season the beef on all sides with coarse salt and black pepper. Heat the vegetable oil in a separate large skillet over medium-high heat. Add the beef and cook, turning, until browned on all sides (including the butt), about 8 minutes. Transfer the beef to a wire rack and let cool.
5. Lay two sheets of plastic wrap on a work surface to form a large rectangle (approximately 55 x 75 cm), with the short side facing you. Lay the prosciutto slices crosswise, overlapping them, on the wrap to form a rectangle slightly longer than the beef and wide enough to completely wrap around the meat, with a slight overlap. You may not need all of the ham.
6. Spread the mushroom mixture over the prosciutto, pressing gently. Trim the beef strings and coat the entire surface with mustard. Place the beef on top of the mushroom mixture, perpendicular to the prosciutto slices. Wrap the beef tightly in the prosciutto, using plastic wrap to help.
7. Twist and tie the ends of the plastic wrap to keep the roast in an even shape. Refrigerate for at least 30 minutes.
8. On a lightly floured work surface, roll out the puff pastry into a 35 x 37 cm rectangle. If using 2 small sheets of dough, press the ends together before rolling and trim if necessary. Brush the dough with beaten egg.
9. Remove the film from the beef and place it on the dough. Carefully wrap the meat in the dough, overlapping the ends at the seam; trim off any excess dough if necessary, then pinch the seams shut. Turn the meat cut side down. Fold the dough over at the two open ends, trimming off any excess.
10. Refrigerate until dough is cold and firm, about 1 hour.
11. Position a rack in the lower third of the oven; preheat the oven to 220°C (425°F). Line a baking sheet with parchment paper or foil. Place the beef seam-side down on the baking sheet and brush the entire surface with a beaten egg. Score the dough with the blunt side of a knife (do not cut the dough) and sprinkle with coarse salt.
12. Bake until crust is crisp and deep golden brown and a thermometer inserted into the center of the beef reads 115°F (43°C) to 125°F (48°C) for medium-rare, 40 to 50 minutes.
13. Transfer to a rack set over a baking sheet and let the meat rest for 15 minutes before slicing. Sprinkle with additional coarse salt and chives.
    
    Note
    
    To help the tenderloin maintain its shape, tie it with kitchen twine every 2.5 cm before frying. Remember to remove the twine before wrapping the beef in the dough!