Mix the cocoa, sugar, vanilla and a splash of the milk into a smooth paste in a bowl.
Pour the remaining milk into a saucepan and place over low heat until it just begins to boil. Whisk the hot milk into the chocolate mixture. Ladle the cocoa into serving cups.
Top with dollops of whipped cream or marshmallows and serve immediately.
Notes
Make it dairy-free! We recommend coconut, cashew or rice milk.