Lamb Sirloin Recipe

Bring to room temperature

Remove the lamb sirloin from the refrigerator 30–45 minutes before cooking so it comes closer to room temperature. Pat dry thoroughly with paper towels.

Season

Rub the entire surface of the lamb with 1 tablespoon olive oil, then rub in minced garlic, chopped rosemary, kosher salt, and black pepper. Let rest for 5–10 minutes to absorb flavors.

Sear and roast

Preheat oven to 400°F (200°C). Heat a heavy ovenproof skillet (cast iron preferred) over medium-high heat until hot. Add remaining 1 tablespoon olive oil. When oil is shimmering, place lamb sirloin fat-side down (if applicable) and sear without moving for 2–3 minutes until well browned. Turn and sear all sides, about 1–2 minutes per side, using tongs. Add 1 tablespoon butter to the pan for flavor and baste the lamb with melted butter for 30–60 seconds.

Finish in oven

Transfer the skillet to the preheated oven. Roast 8–12 minutes for medium-rare (internal temperature 125–130°F / 51–54°C), or longer for desired doneness. Use an instant-read thermometer inserted into the thickest part to check.

Rest

Remove the lamb from the oven and transfer to a cutting board. Tent loosely with foil and let rest 8–10 minutes (internal temperature will rise ~5°F). This helps juices redistribute.

Slice

Slice the lamb sirloin against the grain into 1/4-inch to 1/2-inch slices. Keep warm while you make the pan sauce.

After removing the lamb, return the skillet to medium heat on the stove. If there is excessive fat, spoon off all but about 1 tablespoon. Add the finely chopped shallot and sauté 1–2 minutes until softened and translucent, scraping up browned bits (fond) from the bottom of the pan.

Add the minced garlic and cook 20–30 seconds until fragrant, being careful not to burn.

Pour in the dry red wine to deglaze the pan, stirring and scraping the fond. Bring to a simmer and reduce by about half, 3–5 minutes.

Add the beef or lamb stock, Dijon mustard, and a sprig of fresh rosemary. Simmer until slightly reduced and coating consistency, about 3–5 more minutes.

Turn heat to low. Remove and discard the rosemary sprig. Whisk in the cold cubed butter one piece at a time to emulsify and slightly thicken the sauce. Taste and season with salt and pepper as needed.

Spoon the sauce over sliced lamb or serve on the side.

Arrange sliced lamb on a warmed platter, drizzle with pan sauce, garnish with microgreens or chopped parsley and lemon wedges for squeezing. Serve immediately.