- Preheat oven to 450˚F. Set roast in a roasting pan. Brush roast with mustard, and then sprinkle with salt, pepper and rosemary. Roast 20 minutes, then reduce heat to 325˚F, and continue cooking to desired doneness. Allow about 20 minutes per pound for rare, 25 for medium-rare and 30 for medium (see Note).
- While beef cooks, make horseradish mayonnaise by combining it’s ingredients in a bowl. Cover and refrigerate until needed.
- To prepare asparagus. Cook in boiling water until just tender, about 2 to 3 minutes. Lift asparagus out of the pot and set in ice-cold water. When cold, dry asparagus on a kitchen towel, and then arrange on a serving platter. Place the rest of the ingredients for the asparagus in jar, seal, and shake well combine. Keep this vinaigrette and the asparagus refrigerated until needed.
- When beef is ready, set on a plate, loosely cover and rest 10 to 15 minutes. While it rests, make jus to serve with the meat by set the roasting pan over medium-high heat. Add the stock and bring to a simmer, scraping the bottom of the pan to dislodge the tasty brown bits. Simmer a few minutes and jus is ready.
- To serve, slice the beef and serve it with the jus, horseradish mayonnaise and the asparagus, topped with the vinaigrette.
If desired, just before serving, you could also sprinkle asparagus with a bit lemon zest.
Note: Because roasts can vary in thickness, absolutely always use an instant-read meat thermometer to gauge doneness. A rare roast is done at 120˚F; medium-rare will be 125˚F to 130˚F. Remember that the meat will continue to cook when resting.