Preheat oven to 400°.
Unroll roast; trim fat. Spread minced rosemary, 1/4 teaspoon salt, and garlic into folds of the roast. Reroll roast; secure at 3-inch intervals with heavy string. Sprinkle with 1/4 teaspoon salt and pepper. Drizzle with oil. Secure rosemary sprigs under strings on roast. Place roast on the rack of a broiler pan or roasting pan; insert meat thermometer into thickest portion of roast. Bake at 400° for 1 hour. Increase oven temperature to 425° (do not remove roast from oven). Bake an additional 20 minutes or until thermometer registers 140° (medium-rare) to 155° (medium). Place roast on a platter; cover with foil. Let stand 10 minutes for roast to reabsorb juices. (Temperature of roast will increase 5° upon standing.) Remove string and rosemary sprigs before slicing.
Remove rack from pan. Combine 1/2 cup wine and cornstarch; set aside. Add 1/2 cup wine to drippings in pan; scrape pan to loosen browned bits. Combine drippings mixture and 1 cup wine in a saucepan; bring to a boil. Cook 5 minutes. Add 1/4 teaspoon salt and cornstarch mixture; return to a boil. Cook 1 minute or until thick, stirring constantly. Serve with lamb.
Use a full-bodied, dry red wine such as Cabernet Sauvignon, Merlot, or Cabernet Franc. Increasing the oven temperature for the last 20 minutes browns the lamb.