In a small bowl, whisk together the unsweetened cocoa powder, granulated sugar, and a pinch of salt until there are no lumps. This ensures even dispersion in the milk.

Warm milk and cream

Pour the whole milk and heavy cream into a small saucepan and set over medium-low heat. Warm the liquid until it is steaming and small bubbles begin to form around the edges (do not boil). This should take about 4–6 minutes.

Incorporate cocoa mixture

Whisk about 1–2 tablespoons of the warmed milk into the cocoa-sugar mixture to make a smooth paste (this is a slurry). Then pour the slurry back into the saucepan with the rest of the milk, whisking constantly to combine and prevent lumps.

Add chocolate

Add the finely chopped bittersweet or semisweet chocolate to the saucepan. Continue to whisk over low heat until the chocolate is fully melted and the mixture is smooth and slightly thickened, about 1–2 minutes.

Finish flavoring

Remove the saucepan from heat. Stir in the vanilla extract. Taste and adjust sweetness if desired by adding up to 1 additional teaspoon of sugar, stirring to dissolve.

Serve hot

Ladle the hot chocolate into two warmed mugs (about 1 cup each).

Optional Toppings

Top each mug with a spoonful of whipped cream or a handful of mini marshmallows. Sprinkle a pinch of ground cinnamon or a dusting of cocoa powder or chocolate shavings over the top for garnish.

If you like, toast marshmallows briefly over a kitchen torch or broiler-safe heat source and place one on top for a smoky note. Serve immediately while hot.