In a medium saucepan set over medium-low heat, combine 2 cups whole milk and 1/2 cup heavy cream. Warm gently, stirring occasionally, until small bubbles form around the edges and the mixture is hot but not boiling (about 4–6 minutes).

Whisk cocoa and sugar

In a small bowl, whisk together 1 tablespoon unsweetened cocoa powder and 1 teaspoon granulated sugar with 2 tablespoons of the warmed milk mixture to form a smooth paste. This prevents lumps and helps the cocoa incorporate evenly.

Combine chocolate

Add the cocoa paste back into the saucepan along with 3 ounces finely chopped bittersweet chocolate and a pinch of fine sea salt. Reduce heat to low and stir constantly with a whisk or heatproof spatula until the chocolate is fully melted and the mixture is smooth and slightly thickened (about 2–3 minutes). Do not boil.

Adjust sweetness and texture

Taste and adjust sweetness if desired: add up to 1–2 additional teaspoons granulated sugar if you prefer sweeter hot chocolate. If the drink is too thick, thin with up to 1/4 cup additional warmed milk.

Flavoring & Finish

Add vanilla and espresso (optional)

Remove the saucepan from heat and stir in 1/2 teaspoon pure vanilla extract. If making a mocha, stir in 1 ounce freshly brewed espresso now. Mix until fully incorporated.

Serve

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

Top and garnish

Top each mug with approximately 2 tablespoons whipped cream and sprinkle 1 teaspoon total mini marshmallows between the two drinks (or distribute as preferred). Finish with a light dusting of cocoa powder or grated chocolate over the whipped cream.

Safety and presentation tip

Serve immediately while hot. If reheating later, warm gently over low heat and whisk to restore smooth texture—avoid boiling to prevent separation.