Step 1

Preheat oven to 400 degrees F.

Step 2

Season roast with 3/4 teaspoon salt and 1/2 teaspoon pepper. Heat oil in a large ovenproof skillet (see Tip) over medium-high heat. Add the roast and cook, turning every few minutes, until browned on all sides, about 10 minutes. Remove from heat.

Step 3

Combine butter, shallot, rosemary, and minced garlic; spread on top of the roast. Transfer the pan to the oven. Roast until a thermometer inserted in the center of the meat registers 125-130 degrees F for medium-rare, 35 to 40 minutes. Transfer the roast to a cutting board and let rest for 10 minutes.

Step 4

Meanwhile, whisk grated garlic, yogurt, horseradish, mustard, and lemon juice in a small bowl. Season with the remaining 1/4 teaspoon each salt and pepper. Slice the beef thinly and serve with the sauce.