Layer sliced potatoes in a lightly greased or lines 6-quart slow cooker; top with chopped onion. Stir together broth, salt, and pepper; pour over potatoes and onion. (Broth will not completely cover potatoes and onion.) Cover and cook on HIGH 3 to 5 hours or until potatoes are tender. Mash mixture with a potato masher; stir in half – and – half. Cover and cook on HIGH 20 more minutes or until mixture is thoroughly heated. Ladle into bowls and serve with desired toppings.