Place carrots and onions in a 4- to 5-quart slow cooker. Place beef on top of vegetables. In a small bowl stir together wine, broth, mustard, garlic, salt, thyme, and pepper. Add broth mixture and bay leaf to cooker.
Cover and cook on low-heat setting for 9 to 10 hours or on high-heat setting for 4-1/2 to 5 hours.
Use a slotted spoon to transfer ribs and vegetables to a serving dish, reserving cooking liquid. Discard bay leaf. Skim fat from liquid. Pour some of the cooking liquid over ribs to moisten. Serve with Horseradish Sauce. Makes 6 servings.
In a small bowl, combine sour cream, horseradish, and salt. Cover and chill until ready to serve.