Whisk apple cider, pumpkin purée and pumpkin-pie spice in a large saucepan on high. Bring to a boil, then reduce heat to medium-low. Simmer, stirring occasionally, for 10 min. Strain into a large bowl. Discard purée. Stir rum into pumpkin mixture. Divide among 4 mugs and garnish with dollops of whipped cream. Sprinkle with more pumpkin-pie spice if desired.