This is a great recipe. I Got it from The Best of Fine Cooking Side Dish Magazine. I have made this twice now with fave reviews. Putting it here for safe keeping in case I lose the magazine (which I have been known to do).
Let the roast sit at room temperature for 30 minutes. Meanwhile position a rack in the middle of the oven and heat the oven to 400°F Put a roasting rack in the roasting pan or a heavy-duty rimmed baking sheet. (Line the pan with foil for easier clean-up if you like.).
Season the roast liberally with salt and pepper on all sides. Turn on the exhaust fan. Heat the oil in a large sauté pan over medium-high heat. When the oil is hot, brown the meat well on all sides, including the ends, about 4 minutes per side. Transfer the meat to the roasting pan. Set aside to cool while you prepare the crust.
In a medium bowl, combine the breadcrumbs, shallots, garlic, thyme, marjoram, 1/2 teaspoons salt & 1/4 teaspoons pepper. Pour the melted butter into the breadcrumb mixture; toss to combine.
Using a rubber spatula, smear the top and sides of the beef with the musterd. With your hands, lightly press the breadcrumb mixture into the mustard.
Roast the beef until an instant-read thermometer inserted into the middle part of the mead reads 125°F for medium rare, about 60 minutes for a strip loin roast or 60 to 80 minutes for a top sirloin roast, depending on its thickness. (To keep the crust from over browning start checking on the roast after 30 minutes of cooking, and when the crust is golden brown, tent it with aluminum foil).
Meanwhile make the horseradish-mustard sauce (recipe follows).
Remove the roast from the oven and let the meat rest for 10 to 20 minutes (the meat will continue to cook as it rests) before carving, across the grain, into 1/2 inch thick slices.
CREAMY HORSERADISH-MUSTARD SAUCE: In small bowl, whisk all the ingredients. Let the sauce sit for 20 minutes for the flavors to meld before serving. The sauce can be stored, covered, in the refrigerator for up to 4 days; stir before using.