The main ingredient you’ll need for this dish is a rack of lamb. The sizes of these may vary somewhat, and Musgrave notes that “bigger cuts of lamb will require more cook time.” Conversely, smaller ones will require less time in the oven. She does say, though, that “the rest of the ingredients should be sufficient as long as the rack of lamb is not significantly large” (or small).
In addition to the lamb, you’ll need some mustard — Dijon, particularly. You’ll also need oil, minced garlic, thyme, oregano, salt, and pepper, and then you’ll be all set to start cooking.