Elegance is the word for this main course, especially with the nut butter and wasabi-crusted top. Beef tenderloin is the cut from which filets mignons are portioned, so you and your lucky guests will be eating a tender, great-flavored cut. Armed with an instant-read thermometer and an accurately calibrated oven, any cook can succeed with this recipe—even a novice. Freeze the extra flavored butter and cut slices to top grilled or pan-seared steaks, lamb, or pork.