ROAST BEEF TENDERLOIN WITH CARAMELIZED ONION AND MUSHROOM STUFFING

Steps:

• SERVES 4 TO 6
• The roast can be stuffed, rolled, and tied a day ahead, but don't season the exterior until you are ready to cook it. This recipe can be doubled to make two roasts. Sear the roasts one after the other, cleaning the pan and adding new oil after searing the first roast. Both pieces of meat can be roasted on the same rack.
• FOR THE STUFFING: Process mushrooms in food processor until coarsely chopped, about six 1-second pulses. Heat butter and oil in 12-inch nonstick skillet over medium-high heat until foaming subsides. Add onion, table salt, and pepper; cook, stirring occasionally, until onion begins to soften, about 5 minutes. Add mushrooms and cook, stirring occasionally, until all moisture has evaporated, 5 to 7 minutes. Reduce heat to medium and continue to cook, stirring frequently, until vegetables are deeply browned and sticky, about 10 minutes. Stir in garlic and cook until fragrant, 30 seconds. Slowly stir in Madeira and cook, scraping bottom of skillet to loosen any browned bits, until liquid has evaporated, 2 to 3 minutes. Transfer onion-mushroom mixture to plate and cool to room temperature.
• FOR THE ROAST: Following illustrations 1 and 2, butterfly roast. Season cut side of roast liberally with kosher salt and pepper. Following illustration 3, spread cooled stuffing mixture over interior of roast, leaving 1/2-inch border on all sides; lay spinach on top of stuffing. Following illustrations 4 and 5, roll roast lengthwise and tie.
• In small bowl, stir together 1 tablespoon olive oil, 1 1/2 teaspoons kosher salt, and 1 1/2 teaspoons pepper. Rub roast with oil mixture and let stand at room temperature for 1 hour.
• Adjust oven rack to middle position and heat oven to 450 degrees. Heat remaining 2 tablespoons olive oil in 12-inch skillet over medium-high heat until smoking. Add beef to pan and cook until well browned on all sides, 8 to 10 minutes total. Transfer beef to wire rack set in rimmed baking sheet and place in oven. Roast until instant-read thermometer inserted into thickest part of roast registers 120 degrees for rare, 16 to 18 minutes, or 125 degrees for medium-rare, 20 to 22 minutes.
• FOR THE BUTTER: While meat roasts, combine butter ingredients in small bowl. Transfer tenderloin to cutting board; spread half of butter evenly over top of roast. Loosely tent roast with foil; let rest for 15 minutes. Cut roast between pieces of twine into thick slices. Remove twine and serve with remaining butter passed separately.
• STEP-BY-STEP
• Stuffing and Tying a Tenderloin
• Insert chef's knife about 1 inch from bottom of roast and cut horizontally, stopping just before edge. Open meat like a book.
• Make another cut diagonally into thicker portion of roast. Open up this flap, smoothing out butterflied rectangle of meat.
• Spread filling evenly over entire surface, leaving 1/2-inch border on all sides. Press spinach leaves evenly on top of filling.
• Using both hands, gently but firmly roll up stuffed tenderloin, making it as compact as possible without squeezing out filling.
• Evenly space 8 pieces kitchen twine (each about 14 inches) beneath roast. Tie each strand tightly around roast, starting with ends.