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1
Preheat oven to 200u00b0F (90u00b0C) and position oven rack low enough to fit crown roast in oven. Generously season crown roast all over with salt and pepper. Place roast on a rack set in a rimmed baking sheet and roast until lamb registers 115u00b0F (46u00b0C) on an instant-read thermometer inserted into center of loin, 1 to 1 1/2 hours.
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2
In a heatproof bowl, pour boiling stock or water over apricots, prunes, and pistachios and let steep for 10 minutes. Meanwhile, in a medium skillet, heat 3 tablespoons (45ml) olive oil over medium-high heat until shimmering. Add onion and coriander, lower heat to medium, and cook, stirring, until golden and soft, about 8 minutes. Drain dried fruit and pistachios of any excess liquid. In a large bowl, toss together couscous, apricots, prunes, pistachios, cooked onions, parsley, and remaining 1/2 cup (120ml) olive oil. Season with salt and pepper and keep warm.
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3
Using an immersion blender, blender, or food processor, pulse mint, parsley, and pistachios until roughly chopped. Add 1/4 cup (60ml) olive oil and pulse until herbs and nuts are finely chopped. Stir in remaining 3/4 cup (180ml) olive oil and season with salt and pepper. Set aside.
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4
When lamb reaches 115u00b0F (46u00b0C), remove from oven. Increase oven to highest possible temperature (broil setting on some ovens, or about 500u00b0F/260u00b0C on others) and allow to heat fully. Cover lamb rib bones with foil. Roast lamb, checking temperature every 5 minutes and then more frequently as it approaches doneness, until lamb is browned and an instant-read thermometer inserted into thickest part of lamb registers 125 to 130u00b0F (52 to 54u00b0C) for medium-rare, or 130 to 135u00b0F (54 to 57u00b0C) for medium, about 10 minutes. Let lamb rest for 15 minutes.
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5
Stuff with warm couscous and serve, passing sauce at the table. To carve lamb, slice lamb between rib bones into chops.
