Rub rib rack(s) all over with mixture of rosemary, thyme, and garlic. Sprinkle with freshly ground black pepper. Place in a thick plastic bag with olive oil.
Spread oil around so that it coats the lamb rack(s) all over. Squeeze out as much air as you can from the bag and seal. Place in a container so that if the bag leaks, the container catches the leak.
If you want, place in the refrigerator overnight. Or, if you are not marinating overnight, let lamb rack(s) sit in the rub marinade as it comes to room temperature before cooking.
Remove lamb rack from refrigerator to 1-2 hours before you cook it so that it comes to room temp. (If the meat is not at room temperature it will be hard for it to cook evenly.)
Preheat oven to 400°F, arrange the oven rack so that the lamb will be in the middle of the oven. Score the fat, by making sharp shallow cuts through the fat, spaced about an inch apart..Sprinkle the rack all over with salt and pepper. Place the lamb rack bone side down (fat side up) on the pan.
Wrap the exposed ribs in a little foil so that they don't burn. Roast at 400°F for 7 minutes, then lower the heat to 300°F. Cook for 7-15 minutes longer (depending on the size of the lamb rack, or one of the lamb racks.
if you are cooking more than one), until a meat thermometer inserted into the thickest part of the meat 125°F on a for rare or 135°F for medium rare.
Remove from oven, cover with foil and let rest for 5-10 minutes. Cut lamb chops away from the rack by slicing between the bones. Serve 2-3 chops per person.