Rack of Lamb with Mustard Sauce

Mustard Sauce: In small saucepan, bring stock to boil. Boil for about 6 minutes or until reduced to 1/4 cup (50 mL).

Meanwhile, in small saucepan, heat butter and oil over medium-low heat; cook garlic, shallot and thyme, stirring often, for about 5 minutes or until softened. Increase heat to medium; add vermouth and cook, stirring, for about 2 minutes or until reduced by half. Pour in stock; bring to boil. Remove from heat and stir in Dijon and grainy mustards, salt and pepper. (Make ahead: Let cool; cover and refrigerate for up to 1 day. Reheat before serving.)

Pat dry racks of lamb with paper towel. In large skillet, heat half of the oil over high heat; brown 2 of the racks for about 2 minutes per side. Transfer to large plate. Repeat with remaining oil and racks.

Brush lamb with Dijon mustard; sprinkle tops and sides with mustard seeds, rosemary, salt and pepper. Place, bone side down, on rack in roasting pan or on foil-lined rimmed baking sheet. Roast in 450°F (230°C) oven for about 12 minutes for rare or until desired doneness.

Transfer to cutting board; tent with foil and let stand for 10 minutes. Cut into chops; serve with sauce.