In a large bowl cream the butter and the sugars together until smooth. Add the softened ice cream and mix until a creamy consistency is obtained. Transfer this to a freezer container with a tight fitting lid. Place in the freezer for up to 1 month.
To Serve: Place a heaping 2 tablespoons of the frozen mix in a highball glass or coffee mug. Add 1 to 2 tablespoons dark rum. Pour over the mix 6 ounces of boiling water and stir until the mixture is melted. Sprinkle top with cinnamon or nutmeg and serve forth!