Combine the hazelnuts, breadcrumbs and rosemary in a large bowl.
Arrange the lamb meat side up on a baking sheet. Brush each rack with the mustard, season with salt and pepper and press the hazelnut mixture onto the top of the lamb. Drizzle with the honey.
Roast until the internal temperature of the thickest portion of the lamb reaches 130 degrees (approximately 20-25 minutes). Remove from the oven and allow the lamb to rest for 10 minutes before slicing.
[Note: This recipe results in medium-rare cooked lamb. You may wish to cook the lamb until slightly less rare - medium rare (just pink) would read about 140 degrees when tested with an instant-read thermometer. Allow to rest as directed before carving.]