Prep your tools and ingredients. Chill a medium mixing bowl and whisk (or mixer beaters) in the freezer for 10 minutes. Chop the chocolate if using bars. Set out your extracts and sugar so everything is within reach.

Gently melt the chocolate. Place the chopped chocolate in a heatproof bowl. Heat 1/2 cup of the cream until steaming (microwave or stovetop), then pour it over the chocolate. Let it sit for 1 minute, then stir until smooth and glossy. If needed, microwave in 10-second bursts, stirring between each, until fully melted.

Add flavor and cool the mixture. Stir in the vanilla, a pinch of salt, and 1/2 teaspoon peppermint extract. Taste and add more peppermint extract a drop at a time until it’s minty but not overpowering. Let the chocolate mixture cool to room temperature—slightly warm is fine, but not hot.

Whip the cream. In your chilled bowl, whip the remaining 1 1/4 cups cold heavy cream with the sugar to medium peaks. You want it soft enough to fold easily but firm enough to hold shape. Don’t overbeat or it will turn grainy.

Fold chocolate into cream. Add a large spoonful of whipped cream to the chocolate mixture and stir to lighten. Gently fold in the remaining whipped cream in two or three additions using a spatula. Work slowly, lifting and turning the mixture so you keep the mousse airy.

Portion and chill. Spoon the mousse into small glasses, ramekins, or a serving bowl. Cover and chill for at least 1 to 2 hours, or up to 24 hours. It will set slightly and the flavors will deepen.

Garnish and serve. Right before serving, top with a dollop of whipped cream. Sprinkle with crushed candy canes or peppermint candies, and add chocolate shavings if you like. Serve cold.