Ingredients

• 1 (4-lb.) New York strip roast, preferably prime, untied
• Kosher salt, freshly ground pepper
• 6 garlic cloves, finely grated
• 3 Tbsp. finely chopped rosemary
• 5 Tbsp. extra-virgin olive oil, divided
• 1/2 cup plain whole-milk Greek yogurt
• 1/2 cup sour cream
• 2 Tbsp. prepared horseradish
• 1/2 tsp. finely grated lemon zest
• Warm rolls and cornichons (for serving)

Instructions

1. Lightly score fat cap of roast, spacing cuts about 3/4" apart, with a sharp knife, being careful not to slice into the flesh. Season roast generously on all sides with salt and pepper. Mix garlic, rosemary, and 3 Tbsp. oil in a small bowl and rub all over roast. Loosely cover with plastic wrap and chill at least 12 hours and up to 2 days.
2. Preheat oven to 200°F. Place roast on a wire rack set inside a large rimmed baking sheet. Roast until an instant-read thermometer inserted into the thickest part of meat registers 118°F–120°F for medium-rare, about 2 1/2 hours. Let rest 1 hour (internal temperature will continue to climb to 125°F–130°F).
3. Mix together yogurt, sour cream, horseradish, and lemon zest in a small bowl; season sauce with salt.
4. Heat remaining 2 Tbsp. oil in a large skillet over medium. Cook roast just until browned, about 2 minutes per side. Transfer to a cutting board and thinly slice. Serve with horseradish sauce, rolls, and cornichons.
5. Beef can be roasted and browned 3 days ahead. Cover and chill. Let sit at room temperature 1–2 hours before serving.