Preheat oven to 325°. In an ovenproof Dutch oven, brown lamb in butter and oil in batches. Remove and keep warm. In the same pan, saute carrots and onions in drippings until crisp-tender. Add garlic; cook 1 minute. Gradually add broth and beer. Stir in lamb, potatoes, bay leaves, thyme, rosemary, salt and pepper., Cover and bake 1-1/2 to 2 hours or until meat and vegetables are tender, stirring every 30 minutes. Discard bay leaves, thyme and rosemary. Stir in cream; heat through.