01 - In a saucepan, combine milk, cocoa powder, sugar, and salt. Heat over medium heat, stirring constantly until hot and smooth, approximately 3-4 minutes. Remove from heat and incorporate the vanilla extract.
02 - Evenly divide the warm cocoa mixture between two large heatproof glasses.
03 - Slowly pour 1/2 cup of chilled root beer into each glass, allowing the effervescence to subside.
04 - Add one scoop of vanilla ice cream to each glass.
05 - Pile mini marshmallows on top of the ice cream and briefly toast with a kitchen torch until golden brown for added flavor.
06 - Serve immediately with a straw and a long spoon.