Ingredient: Dijon mustard, divided

How To Prepare
Preheat oven to 450°F.
Mix potato flour, 1/2 teaspoon oil, 1/2 teaspoon rosemary, and 1/8 teaspoon pepper in a small bowl.
Heat the remaining 1 teaspoon oil in a large ovenproof skillet over medium-high heat. Add lamb, meat-side down, and sear until browned, about 1 1/2 minutes. Turn it over and spread 2 teaspoons mustard over the meat. Sprinkle the potato flour over the mustard. Transfer the lamb to the oven and roast until a thermometer inserted in the center registers 140°F for medium-rare, 15 to 20 minutes. Transfer to a plate and tent with foil to keep warm.
Return the pan to medium-high heat (be careful: the handle will still be hot). Add shallots, the remaining 1/2 teaspoon rosemary and 1/8 teaspoon pepper and cook, stirring constantly, until starting to soften, about 1 minute. Stir in lentils, apple, celery, broth (or water), vinegar and the remaining 1 teaspoon mustard; bring to a lively simmer. Cook, stirring occasionally, until the liquid is slightly reduced and the celery and apple are starting to soften, about 4 minutes. Cut the lamb into 8 chops and serve over the lentils.
TIPS & NOTES
Tip: To serve 4 people, look for a rack of lamb that has 8 chops. If you can find one that’s been “Frenched” (meat cut away at the tips, exposing the bone) and trimmed, you will only need a 1-pound rack. Otherwise, look for a 1 1/2-pound rack and ask your butcher to prepare it for you.