A tall glass.
Two packets of hot cocoa mix.
One scoop of ice cream, chocolate or vanilla.
Vodka or brandy of choice*.
Put cocoa mix, scoop of ice cream, and a splash of vodka in the bottom of the glass. Pour boiling water over ingredients. Mix with a spoon or fork until the mix is completely dissolved and the ice cream is broken up into a rich foam at the top of the glass. Add marshmallows. Enjoy.
*Assuming, of course, that you're at least 21 and drink your cocoa responsibly.