Preparation

Make the stuffing

• Position a rack in the center of the oven and heat to 350°F. Arrange the bread in a single layer on one or two large rimmed baking sheets and toast until dried and crisp, about 15 minutes. Cool to room temperature on a rack.
• Put the mushrooms in a small bowl and cover with 1/2 cup boiling water. Soak until softened, about 20 minutes. Strain the mushrooms over a bowl, squeezing them to extract more liquid. Reserve the liquid and mushrooms separately, and coarsely chop the mushrooms.
• Cook the bacon in a large skillet over medium heat until browned, about 8 minutes. Transfer the bacon to a paper-towel-lined plate. Add the leeks to the skillet, and cook, stirring occasionally and adjusting the heat as necessary, until very soft, about 10 minutes. Coarsely chop the bacon and transfer it to a large bowl. Add the leeks, bread, mushrooms, cheese, parsley, thyme, 1/2 tsp. salt, and 1/2 tsp. pepper. In a small bowl, whisk the cream, eggs, and the reserved mushroom soaking liquid, and pour over the bread mixture. Toss well, let sit for 5 minutes, and toss again. cover and chill for at least 30 minutes and up to 1 day.

Wrap the beef

• Pat the tenderloin dry and season well with salt and pepper.
• lay some plastic wrap on a work surface so that it measures at least 20×20 inches; overlap a couple of pieces of plastic wrap as needed. Put parchment paper at least the length of the tenderloin over the plastic wrap and spray it with cooking spray or lightly oil it. Press the stuffing mixture over the parchment into a rectangle measuring about 12×14 inches.
• 牛肉在填料的中心位置。lift the plastic to wrap the parchment and stuffing around the beef, rolling it like a sushi roll and encasing the beef completely. Wrap tightly in the plastic wrap, twisting the excess plastic on each end to compress the roast. Tuck the twists under the roast to keep snug. Chill for at least 1 hour and up to 1 day. Longer is better as it helps everything to firm up.

Start the sauce

• Combine the vinegar, wine, shallot, bay leaf, and sugar in a small saucepan. Bring to a simmer over medium-high heat, and cook, stirring occasionally, until reduced by nearly half, 10 to 12 minutes. Set aside. The sauce may be made up to this point 1 day ahead; cover and refrigerate.

Roast the beef and finish the sauce

• Position a rack in the center of the oven and heat to 375°F. Line a roasting pan with parchment and set a rack in it. Unwrap the plastic from the beef but leave the parchment on. Tie the roast with butcher’s twine in about 5 even intervals. Place the roast on the rack. Roast to medium rare (125°F), about 60 minutes. Let rest for 15 minutes. (If meat is bulging in the center, put a kitchen towel over it and gently press on the roll to reshape it.)
• Remove the bay leaf from the sauce and gently reheat the sauce over low heat. Swirl in the cold butter just until it melts to thicken the sauce. Remove from the heat. Season to taste with salt and pepper.
• Trim any uneven edges of the roast. Slice the roast through the parchment with a very sharp knife (serrated works well here) into thick slices, removing the twine as you go. The pieces may crumble a bit, so you may need to reassemble them on the serving plates or platter. Remove the parchment and serve with the sauce, garnished with the parsley.