Pour the apple cider into a large pot or Dutch oven and place it over medium heat.
Stir in the brown sugar until it dissolves completely. Add the cinnamon sticks, whole cloves, whole allspice, and sliced orange (and apple, if using) to the pot.
Bring the mixture to a gentle simmer, stirring occasionally. Reduce the heat to low, cover, and let it simmer for 20-30 minutes to allow the spices to infuse the cider.
Taste the cider and adjust sweetness by adding more brown sugar if desired. If using optional spices like star anise or a pinch of nutmeg, add them now and simmer for an additional 5 minutes.
Remove the pot from the heat. Use a slotted spoon or fine mesh strainer to remove the spices, orange slices, and apple slices (if used) from the cider.
Ladle the spiced apple cider into mugs. Garnish with a cinnamon stick or orange slice if desired. Serve warm and enjoy your cozy spiced apple cider!