In slow cooker, combine apple juice, apricot nectar, brown sugar and allspice. Cover and cook on LOW for 5 hours.
Just before serving, heat butter and cinnamon liqueur in a small saucepan or microwave. Spoon 1/2 tablespoon into mug or heatproof cup.
Add 3/4 cup apple juice mixture. Garnish with orange slices, if desired. Serve immediately.