Ingredients

• 1/2 cup (1 stick) unsalted butter
• 2 ounces bittersweet chocolate, chopped
• 1/2 cup (packed) light brown sugar
• 1 teaspoon ground cinnamon
• 1/8 teaspoon kosher salt
• 3/4 cup dark rum
• 1/2 cup heavy cream
• Freshly grated nutmeg (for serving)

Instructions

1. Melt butter and chocolate in a medium heatproof bowl in short bursts in the microwave, stirring after each burst, or set over a saucepan of barely simmering water (do not let water touch bowl), stirring, until smooth. Remove from heat and whisk in brown sugar, cinnamon, and salt.
2. Bring 2 1/2 cups water to a boil in a medium saucepan. Remove from heat and whisk in rum and chocolate mixture until combined.
3. Using an electric mixer on medium-high speed, beat cream in a medium bowl until soft peaks form.
4. Reheat hot chocolate, if needed, then divide among mugs. Top generously with whipped cream and nutmeg.