Preheat the slow cooker if necessary; see the manufacturer's instructions. Add all the ingredients to the slow cooker pot, cover with the lid and cook on high for 1 hour.
Reduce the heat and cook on low for 2–3 hours, or set to auto for 3–4 hours, until piping hot. Stir, then ladle into heatproof tumblers. Add orange wedges and curls to decorate, if liked.