In bowl and with fork mash together garlic, oil, salt, peppercorns, thyme and mustard to form paste. Spread evenly over curved side of roast. Lay rosemary sprigs over curved side of roast. Wrap kitchen twine around roast and rosemary and tie tightly. Place on platter; cover with plastic wrap and refrigerate for 24 hours.

Insert rotisserie rod lengthwise through centre of roast to balance; secure firmly with clamps. Position on 3-burner barbecue over drip pan and light rear heat about 325F for 2-1/2 hours or to desired doneness.

Transfer to cutting board; tent with foil and let stand for 30 minutes.

Remove string and rosemary. Set roast, bone side up; holding bones, cut along underside of bones to remove bones, then cut between bones to separate. Set meat seasoned side up; slice thinly across the grain. Makes 10 to 12 servings.