In a small saucepan, heat the milk over medium heat until it's warm but not boiling.
Once the milk is warm, whisk in the unsweetened cocoa powder, granulated sugar, vanilla extract, and a pinch of salt. Continue whisking until the cocoa powder and sugar are fully dissolved and the mixture is smooth and well combined.
Taste the hot chocolate and adjust the sweetness to your liking by adding more sugar if desired.
Once the hot chocolate is heated through and well mixed, remove the saucepan from the heat and pour the hot chocolate into mugs.
Top each mug of hot chocolate with a generous handful of marshmallows.
Serve the Hot Chocolate with Marshmallows immediately, and enjoy the cozy and indulgent flavors!