To make the marinade: whisk the lemon juice, mustard, rosemary, garlic, and 1 teaspoon of the salt together in a medium bowl. Gradually whisk in the oil and season with pepper.
Transfer the marinade to a large sealable plastic bag. Put the lamb chops in the bag, seal, and shake vigorously to evenly coat the meat. Marinate at room temperature for 1 hour or in the refrigerator for at least 4 hours and up to 12.
Remove the chops from the marinade and transfer them to a plate. Discard the marinade. Using a spoon, lightly scrape the remaining marinade off the chops and pat them dry.
Preheat a large cast-iron grill pan over medium heat for 3 to 5 minutes. Raise the heat to medium-high. Season the chops with salt. Place 2 chops on the grill pan, and cook until the chops have distinctive grill marks, about 3 minutes. To make crosshatched grill marks, re-position the chops, moving them about 45 degrees on the ridged pan, and continue to cook about 3 minutes more. (The chops will have only cooked on one side at this point.) Set the chops aside and repeat with the remaining 2 chops. Return the first set of chops to the pan to cook them on the other side. Reduce the heat to medium low, and cook the chops until medium-rare, about 2 minutes. Repeat with the other chops. Let the chops rest for about 5 minutes and serve.
This is the perfect workday-week recipe. In the morning before work, shake the lemony marinade and lamb chops in a plastic bag, and then store it in the refrigerator for the day. When you come home, you'll have ready-to-grill lamb chops waiting for you.
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