Spray 5-quart slow cooker with cooking spray. In slow cooker, mix beef, mushrooms and garlic. In medium bowl, mix broth, wine, flour, chopped rosemary, salt and pepper with wire whisk until blended. Pour over beef mixture.
Cover; cook on Low heat setting 10 hours or until beef is tender and sauce is thickened.
Heat mashed potatoes as directed on package; stir in sour cream. Serve beef with mashed potatoes. Garnish with rosemary sprigs.