Warm the milk in a large saucepan over medium-low heat, stirring occasionally, until steaming but not boiling, about 6 to 8 minutes.

Add the white chocolate chips and whisk until fully melted and smooth.

Stir in green food coloring a drop at a time until the cocoa reaches an even, bright green.

Whisk in the vanilla extract.

Ladle the hot cocoa into 6 mugs.

Top each mug with a swirl of whipped cream and one heart-shaped marshmallow floating on top.

Serve immediately while hot.