Roasted Lamb With Fresh-Herb Sauce

Ingredients

1 (7- to 8-lb.) bone-in leg of lamb, trimmed and tied

1 large shallot, roughly chopped (about 1/2 cup)

1 tsp. Dijon mustard

1/4 tsp. crushed red pepper

1 Tbsp. grated lemon zest

5 Tbsp. fresh lemon juice (from 2 lemons), divided

8 garlic cloves, divided

1 3/4 tsp. kosher salt, divided

1 3/4 tsp. black pepper, divided

1 3/4 cups olive oil, divided

1 cup chopped fresh parsley, plus more for garnish

1 cup chopped fresh mint, plus more for garnish

Lemon slices, to serve

Directions

1. Preheat oven to 450°F with rack 8 inches from heat source.
2. Place a wire rack in a large roasting pan; top with lamb, and pat dry. Let stand at room temperature for 45 minutes.
3. Meanwhile, pulse shallot, mustard, red pepper, lemon zest, 3 tablespoons of the lemon juice, 4 of the garlic cloves, and 1 teaspoon each of the salt and black pepper in a food processor until roughly chopped, about 10 pulses.
4. With processor running, gradually add 1 cup of the oil, processing until smooth. Transfer 1/2 cup of the shallot mixture to a small bowl, and set aside. Cover remaining shallot mixture in food processor bowl, and set aside.
5. Cut 1-inch slits all over lamb. Finely chop remaining 4 garlic cloves; stir into reserved 1/2 cup shallot mixture. Rub shallot-garlic mixture over lamb, and sprinkle with remaining 3/4 teaspoon each salt and pepper.
6. Bake lamb in preheated oven for 20 minutes. Reduce the oven temperature to 300°F, and bake until a thermometer inserted into thickest portion of lamb registers 130°F, 1 hour and 20 minutes to 1 hour and 30 minutes.
7. Without removing lamb from oven, increase oven temperature to broil, and broil until well browned, 5 to 10 minutes. Remove lamb from oven, and cover loosely with aluminum foil. Let rest 20 minutes. (Temperature will continue to rise to 145°F.)
8. While lamb rests, add parsley and mint to shallot mixture in food processor; pulse until herbs are finely chopped and incorporated, about 20 pulses. With processor running, gradually add remaining 3/4 cup oil and 2 tablespoons lemon juice, processing until incorporated. With processor running, gradually add 1 to 2 tablespoons water until sauce reaches desired consistency.
9. Thinly slice lamb against the grain, discarding bone or reserving for another use. Serve sliced lamb with herb sauce. Garnish with lemon slices and herbs.