Combine chocolate, heavy cream, and sugar in a small saucepan over medium-low heat and whisk to combine.

Whisk constantly until chocolate is melted and mixture is smooth (don't turn up the heat to speed up the process, heat that's too high will give you grainy results).

Once the chocolate is completely melted, slowly drizzle milk mixture into the saucepan while whisking constantly. I do this slowly, adding about 2 Tablespoons at a time and making sure the milk is completely incorporated and the mixture has time to regain temperature before adding more.

Once all milk has been added, whisk a bit longer until mixture is thoroughly heated (I look for steam coming off the pot or will hover my hand over the pot to make sure I can feel the heat radiating from it — the milk can cool the mixture quickly and you need to give it a bit of time to warm or your drink won’t be!).

Remove from heat and stir in vanilla extract and a pinch of salt.

Pour into heatproof mugs and serve warm, preferably topped with marshmallows!