1. Make the Buttered Rum Batter: In a mixing bowl, beat butter and brown sugar until light and fluffy. Beat in ice cream and cinnamon, then spoon into a large mason jar or Tupperware container. Store in freezer until mostly hardened, about 2 hours (or store there until you’re ready to serve drinks).
2. Make the Drinks: In a large saucepan, heat cider until boiling, stirring occasionally. Remove from heat and pour into a pitcher or easy-to-serve container.
3. Place about 2 tbsp of the buttered rum batter into each mug. Fill about 1/3 of the way up with rum, then top with hot apple cider. Stir and serve.
BUTTERED RUM BATTER
1 c. butter, softened
3/4 c. packed brown sugar
2 c. vanilla ice cream, softened
2 tsp. cinnamon