1) To make the marinade, whisk the lemon juice, mustard, rosemary, garlic, and one teaspoon of the salt together in a medium bowl. Gradually whisk in the oil and season with pepper.
2) 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 one hour or in the refrigerator for at least 4 hours and up to 12.
3) 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.
4) 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 two chops on the grill pan and cook until the chops have distinctive grill marks, about three minutes.
5) To make crosshatched grill marks, re-position the chops, moving them about 45° on the ridged pan, and continue to cook about three minutes more. (The chops will have only cooked on one side at this point.) Set the chops aside and repeat with the remaining two chops.
6) 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 two minutes. Repeat with the other chops. Let the chops rest for about five minutes and serve.
Cook's note: 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.