Preparation Toast spices with salt in a dry 10-inch heavy skillet over medium-low heat, stirring occasionally, until mustard seeds begin to pop, 3 to 5 minutes. Cool completely, then grind in grinder. Preheat oven to 350°F with rack in middle. Pat beef dry, then rub spice mixture all over it (including ends). Heat oil in same skillet over high heat until it shimmers. Brown beef on all sides, about 10 minutes total. Transfer beef to a small roasting pan and roast until an instant-read thermometer inserted diagonally 2 inches into center of meat registers 120°F for medium-rare, 25 to 30 minutes. Transfer beef to a cutting board and let stand 10 minutes (internal temperature will rise to about 130°F). Cut off string and slice beef. Serve warm or at room temperature. Cooks' note:Beef can be rubbed with spice mixture 1 day ahead and chilled. Let stand at room temperature 30 minutes before browning.
Preparation Toast spices with salt in a dry 10-inch heavy skillet over medium-low heat, stirring occasionally, until mustard seeds begin to pop, 3 to 5 minutes. Cool completely, then grind in grinder. Preheat oven to 350°F with rack in middle. Pat beef dry, then rub spice mixture all over it (including ends). Heat oil in same skillet over high heat until it shimmers. Brown beef on all sides, about 10 minutes total. Transfer beef to a small roasting pan and roast until an instant-read thermometer inserted diagonally 2 inches into center of meat registers 120°F for medium-rare, 25 to 30 minutes. Transfer beef to a cutting board and let stand 10 minutes (internal temperature will rise to about 130°F). Cut off string and slice beef. Serve warm or at room temperature. Cooks' note:Beef can be rubbed with spice mixture 1 day ahead and chilled. Let stand at room temperature 30 minutes before browning.