In a small saucepan, boil the wine and shallots until the liquid is reduced to 1/4 cup, about 5 minutes. Reduce the heat to medium; stir in the whipping cream. Simmer, stirring often, until the sauce thickens, about 12 minutes. Add the mustard and rosemary; simmer for 2 minutes. Season with salt and pepper.
Preheat the oven to 400 degrees . Rub the lamb with the cut garlic; season racks. In a large skillet, cook 2 racks of lamb, fat side down, over medium-high heat, until golden-brown, about 4 minutes. Turn and cook 2 minutes longer. Transfer racks, fat side up, to a rimmed baking sheet. Repeat with the remaining rack of lamb. Roast the racks to desired doneness, about 22 minutes for rare, 25 minutes for medium and 30 minutes for medium-well. Let rest for 5 minutes before cutting into chops.
Serve the lamb chops with warm rosemary-mustard sauce.