Trim excess fat and cut between bones of lamb to expose ribs. In small bowl, combine rosemary, thyme, lavender, salt, pepper, lemon zest, and olive oil to make a paste. Smear this over the entire rack, massaging meat well. Marinate, refrigerated, in covered dish for 4 to 6 hours. When ready to cook, allow meat to come to room temperature. Preheat oven to 400 F

Select cast iron or other ovenproof pan large enough to accommodate the rack and heat it on stovetop on high heat. Sear rack on all sides (including ends) for 1 to 2 minutes each side. Transfer pan and lamb to preheated oven and roast for 12 minutes for medium rare. Remove from oven and allow to rest, covered, for 10 minutes while you prepare the sauce.

In small saucepan, combine blueberries, honey, water, and lavender; simmer for 5 minutes. Add red wine and simmer for 2 to 3 minutes more. Add mixture to food processor and blitz. Strain solids through sieve and discard. Return sauce to saucepan and simmer to reduce slightly. Keep warm.

To serve, add a few tablespoons of sauce to each of 4 plates, carve meat between ribs, and place 2 ribs over sauce on each plate.