Chilling the meat overnight and slicing it thinly the next day gives the rub more time to flavor the meat. This is a great make-ahead dish for parties; serve on toasted baguette with horseradish sauce and arugula.
Preheat oven to 475°.
Combine the first 6 ingredients; massage mixture evenly onto roast. Place roast in a small roasting pan; bake at 475° for 20 minutes, turning after 10 minutes.
Reduce oven temperature to 300° (do not remove roast from oven); bake an additional 30 minutes or until a thermometer registers 120°. Remove roast from oven, and place on a cutting board or work surface. Let rest at room temperature for 30 minutes; roll roast in chopped fresh tarragon.
Wrap roast in parchment paper, then in plastic wrap, and refrigerate for 8 hours or overnight. Cut into very thin slices for hors d'oeuvres.