Beware of the unbelievable smell this will leave in your kitchen. Keep it warm in a crock pot for parties.
Combine cider, cinnamon stick, cloves, orange slice, lemon slice, and nutmeg in a medium saucepan; bring to a boil. Cover, reduce heat, and simmer 20 minutes. Strain cider mixture through a sieve into a bowl and discard solids. Garnish each serving with one cinnamon stick and a thin slice of apple, if desired.