Prep time: 15 minutes
Total time: 3 ½ hours
1 pound|450 grams mixed mushrooms
1 (2-pound|910 gram) piece beef tenderloin
kosher salt, to taste
4 tablespoons|60 ml olive oil
⅓ cup|90 grams Dijon mustard
2 tablespoons unsalted butter
3 garlic cloves, minced
1 medium shallot, minced
1 tablespoon minced fresh thyme
8 slices prosciutto
1 (14-ounce|400 gram) piece puff pastry, defrosted
1 large egg, lightly beaten
- Pulse the mushrooms in the bowl of a food processor until finely chopped and set aside.
- Season the beef all over with salt. Heat 2 tablespoons of the oil in a large skillet over medium-high and cook the meat, turning as needed, until browned all over, about 10 minutes. Transfer to a plate, then brush all over with the mustard. Refrigerate for 30 minutes, then remove any strings that may be on the meat.
- While the skillet is still hot, throw in the butter and the remaining oil. Once the butter has melted, stir in the garlic and shallot and cook until soft, about 3 minutes. Add the chopped mushrooms and cook, stirring, until the liquid has released, 5 to 7 minutes. Stir in the thyme, season with salt and pepper, and cool completely.
- Heat the oven to 425°F. Lay a sheet of plastic wrap down on a clean work surface. Shingle the prosciutto over the top, then spread the mushrooms over in an even layer. Place the filet on the end closest to you, then, using the plastic wrap to help, roll the meat into the prosciutto and mushrooms. Tuck the sides in and refrigerate for 15 minutes.
- Lay the puff pastry out on a clean work surface and gently roll it into a 12-inch square. Remove the plastic wrap from around the beef and place it on the end of the puff pastry closest to you. Brush the edges of the puff pastry with the egg and roll the beef tightly in the puff pastry, trimming and tucking in the ends. Place on a baking sheet and refrigerate for 20 minutes.
- Brush the puff pastry all over with the egg and bake until medium-rare or a thermometer inserted reads 120°F, 40 to 45 minutes. Let the meat rest for at least 10 minutes before slicing and serving.
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