Step 1

Heat the milk, sugar, cocoa powder and salt in a medium saucepan over medium-low heat. Cook, whisking, until the sugar dissolves and the mixture is smooth and steaming with tiny bubbles around the edge of the pan, 8 to 10 minutes.

Step 2

Add the chocolate to the pan; whisk until fully dissolved and smooth. Keep warm.

Step 3

Put the mini marshmallows in a microwave-safe bowl and microwave until puffy, 10 to 20 seconds. Stir with a fork until smooth, then let cool slightly.

Step 4

Pour the hot cocoa into mugs. Using the fork, lift up some of the melted marshmallow and drape it over each mug, zigzagging strands of marshmallow across the top.