Dinner: Porcini-Crusted Beef Tenderloin with Truffle Butter Sauce

Recipe by Alexis Touchet Mushrooms and beef have long been an inspired combination, and here they're joined in a particularly sophisticated way. Dried porcini mushrooms grind to a powder in no time in a blender and add a subtle woodsiness to the beef, wh

Ingredients

1 (6- to 6 1/2-pound) whole beef tenderloin, trimmed of fat, silverskin, and the chain (see Cooks' Notes); or a 5- to 5 1/2-pound well-trimmed tenderloin roast
Salt
Freshly ground black pepper
4 tablespoons olive oil, divided
1/2 ounce (about 1/2 cup) dried porcini mushrooms, ground to a powder in a blender
1/4 cup (2 ounces) black-truffle butter, softened
1/4 cup all-purpose flour
1 pound crimini (baby bella) mushrooms, trimmed and quartered into wedges
3 cups beef stock or low-sodium broth, divided
1/2 cup chopped scallion greens
Special equipment: Kitchen string; large heavy roasting pan; instant-read thermometer

Instructions

Make a deep cut into the top side of tenderloin, about 4 inches from tail end, to facilitate folding the tail end under the roast to give the meat a more uniform thickness. Tie roast at 1-inch intervals with kitchen string.
Heat oven to 350 °F with rack in middle.
Pat tenderloin dry and sprinkle all over with 1 teaspoon each salt and pepper, rubbing into meat.
Set roasting pan over 2 burners, then add 3 tablespoons oil and heat over medium-high heat until shimmering. Brown tenderloin on all sides, about 10 minutes.
Sprinkle porcini powder evenly on top of tenderloin and roast in oven until thermometer inserted diagonally 2 inches into center of thickest part of meat registers 120 °F, 30 to 40 minutes.
Toward end of roasting tenderloin, stir together truffle butter and flour. Heat remaining tablespoon oil in a 12-inch heavy skillet over medium-high heat until shimmering, and sauté mushrooms with 1/4 teaspoon each salt and pepper until liquid released by the mushrooms evaporates and mushrooms are tender and golden, 10 to 12 minutes.
Add 2 cups stock to skillet and simmer, stirring up brown bits, 1 minute. Remove skillet from heat.
Transfer tenderloin to a cutting board and let stand 15 minutes (internal temperature will rise to about 130 °F for medium-rare).
Set roasting pan over 2 burners and add remaining 1 cup stock. Bring to a boil, scraping up brown bits, then pour stock into mushroom mixture in skillet.
Bring mushroom mixture to a boil and whisk in truffle butter mixture, bit by bit. Reduce heat and simmer, whisking occasionally until thickened, about 2 minutes. Stir in scallion greens and salt and pepper to taste.
Cut tenderloin into 1/2-inch-thick slices, discarding string, and serve with sauce.