Heat the apple cider. Mix all ingredients in glass or mug. Garnish with cinnamon stick and split apple rounds.
This is the basic recipe. Easily scalable and tweaked—and open for improvisation: Use a proportion of hard cider or add apple brandy or Calvados. Use bourbon instead of rum. Add a few dashes of cinnamon-flavored spirits, such as schnapps or vodka. Use ginger beer or add a few dashes of ginger liqueur. Emphasize the citrus with a few dashes of triple sec or other orange-flavored liqueur. Try it cold, instead of hot.