Filet de Bœuf en Croûte

Instructions

1. 1
   To get things started, tie the tenderloin with kitchen twine if necessary to secure a perfectly uniform cylindrical shape. Season it aggressively with coarse salt and cracked black pepper on all sides.
2. 2
   Heat the olive oil in a large skillet over very high heat. Sear the beef for about 1 to 2 minutes per side, quickly searing the ends too, until a beautiful brown crust develops. Remove from the heat, snip off the twine, and brush all over with Dijon mustard while hot. Let cool.
3. 3
   In the same skillet over medium heat, melt the butter and sauté the chopped shallots and minced garlic for 3 minutes. Stir in the incredibly fine-mined mushrooms with a pinch of salt.
4. 4
   Cook the mushrooms for 12 to 15 minutes, stirring frequently, until all the moisture they release has completely evaporated, leaving a dry, intensely concentrated paste (duxelles). Stir in the pâté if using, remove from heat, and let cool completely.
5. 5
   Lay out a large sheet of plastic wrap on your clean workspace. Arrange the prosciutto slices on top, overlapping them slightly to construct a solid rectangular blanket large enough to completely encase the beef.
6. 6
   Spread the cooled mushroom duxelles evenly across the prosciutto layer.
7. 7
   Place the seared beef cylinder right in the center and, using the plastic wrap as a guide, roll the prosciutto and mushrooms tightly up and around the meat. Wrap the cylinder firmly in the plastic wrap like a tight sausage and chill in the refrigerator for 30 minutes to set its shape.
8. 8
   Preheat your oven to 200°C (400°F). Roll out your cold sheet of puff pastry onto parchment paper.
9. 9
   Carefully unwrap the chilled beef log and place it in the center of the pastry sheet. Fold the pastry over the meat, trim any excessive bulk, and seal the edges tightly using a brush of water or egg wash.
10. 10
    Transfer the log, seam-side down, onto a parchment-lined baking sheet. Use your pastry scraps or a lattice cutter to design a beautiful enrejado pattern over the top surface, mirroring the file image.
11. 11
    Brush the entire puff pastry exterior thoroughly with the egg yolk wash, and poke two small slits on top to act as steam chimneys.
12. 12
    Bake at 200°C for 30 to 35 minutes until the pastry is deeply golden-brown and intensely crisp. If using a meat thermometer, the core should read 52-54°C (125-130°F) for an ideal medium-rare finish.
13. 13
    Remove from the oven and allow it to rest undisturbed for 10 minutes before carving into thick, majestic slices with a sharp serrated bread knife.