• prep: 40 min
• cook: 0 hr
• total: 40 min

servings:

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, while the truffle butter enriches the sauce with its heady aroma. Black-truffle butter is the best deal going. It gives you tremendous flavor at an affordable price, a fraction of the cost of a fresh black truffle.

• 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
• Kitchen string; large heavy roasting pan; instant-read thermometer

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