Combine vinegar, 2 teaspoons rosemary, and minced garlic in a large zip-top plastic bag.
Add the lamb to bag, and seal. Marinate in refrigerator for at least 6 to 12 hours, turning occasionally.
Preheat oven to 45
Remove lamb from bag, reserving marinade.
Sprinkle lamb with pepper.
Combine the breadcrumbs and 1 teaspoon chopped rosemary, and pat breadcrumb mixture into meaty side of lamb.
Place lamb, meat side up, on a jelly-roll pan coated with cooking spray. Insert a meat thermometer into the thickest part of lamb, making sure not to touch bone.
Bake lamb at 450 for 20 minutes or until the meat thermometer registers 145 (medium-rare) or until the lamb is desired degree of doneness.
Heat olive oil in a large nonstick skillet over medium-high heat; add shallots, and saut for 4 minutes.
Add white wine and reserved marinade, and bring to a boil. Reduce heat, and simmer, uncovered, 8 minutes or until liquid almost evaporates.
Add chicken broth, and bring to a boil. Reduce heat, and simmer, uncovered, until reduced to 1/3 cup (about 5 minutes).
Combine honey and cornstarch, and add to the broth mixture. Bring to a boil, and cook for 1 minute, stirringconstantly.
Slice rack into 8 chops.
Serve sauce with lamb; garnish with thyme sprigs and red grapes, if desired.
Note: You can use 3/4 cup low-salt chicken broth and omit the wine, if desired.
