Barbacoa-Spiced Easter Lamb

Place lamb, fat-side up, on a cutting board; use a knife to score the surface 1/4-inch deep in a crosshatch pattern. After scoring, poke all over with the knife, about 2 inches deep on both sides.

Combine salt, chili powder, black pepper, ancho chile, chipotle, oregano, cinnamon, and garlic powder in a large bowl. Squeeze in orange juice, lemon juice, and lime juice; whisk together thoroughly. 

Place lamb into the bowl; turn over several times to coat completely. Transfer to the refrigerator and marinate, uncovered, for 24 to 48 hours, turning at least once halfway through.

Preheat the oven to 475 degrees F (245 degrees C). 

Remove the rack from a roasting pan and scatter onions into bottom. Place the rack back on.

Toss potatoes, carrots, olive oil, minced garlic, and salt into a bowl and stir until evenly coated. Transfer to the pan, and space evenly around the outside on top of the rack. Place lamb, fat side up, in the center of rack. Pour chicken stock into the bowl used to marinate the lamb; give it a quick stir and pour all of the liquid into the bottom of the pan.

Place in the preheated oven, and immediately turn temperature down to 300 degrees F (150 degrees C).

Roast until internal temperature in the center of largest muscle reads 135 degrees F (57 degrees C) for medium doneness, about 3 hours. Internal temperature will rise up to 5 degrees while lamb rests, for a final temp of about 140 degrees F (60 degrees C). Roasting time will depend on size of lamb, so start to test with a thermometer after 2 hours, or roast with a probe thermometer inserted throughout.

Remove lamb to a plate or cutting board and cover loosely with foil. Let rest at least 30 minutes before slicing.

Meanwhile, transfer vegetables to a serving platter and keep warm. Pour pan jus into a large measuring cup. Wait for fat to rise to the surface; skim off fat and discard. Serve jus on sliced lamb.