Add sugar, cocoa, milk, and 1 1/2 cups marshmallows in a saucepan.
3 tbsp sugar, 4 teaspoons unsweetened cocoa powder, 4 cups milk, 1 ½ cups mini marshmallows
Cook over medium-low heat, string occasionally until all marshmallows are melted and mixture is hot, but not boiling or bubbly. It will get frothy due to the milk and that's okay.