How to Make It
In a small bowl, combine 2 tablespoons of the oil with the garlic, shallot and herbs. Lay the loins on a work surface, fat side down, and season with salt and pepper. Spread the herb paste all over the lamb. Roll each loin over the tenderloin and rib apron to make a neat roulade. With butcher's twine, tie the meat at 1-inch intervals. Season the lamb with salt and pepper.
Preheat the oven to 350°. In a 12-inch skillet (preferably cast-iron), heat the remaining 1 tablespoon of olive oil until shimmering. Add the lamb loins and cook over moderate heat, turning, until browned all over, about 20 minutes total.
Transfer the skillet to the oven and roast the loins for 10 minutes, until an instant-read thermometer inserted in the thickest part registers 125°. Transfer the loins to a carving board to rest for 10 minutes.
Cut off the strings. Carve the loins into 1-inch-thick slices and serve.
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