Melt 7 oz (200 grams) of dark baking chocolate, broken into pieces, in a double boiler with 3 to 4 tablespoons of water. Stir until smooth, then let cool slightly.

Carefully separate the 6 egg whites from the yolks and place them in two separate mixing bowls (make sure no yolk gets into the whites, or they won’t whip properly).

Add the cooled melted chocolate, the juice of half an orange, and 1 tablespoon of rum to the bowl with the 6 egg yolks. Beat vigorously with a mixer until well combined.

With a clean, grease-free whisk, beat the 6 egg whites with a very small pinch of salt until stiff peaks form.

Using a spatula, gently fold the beaten egg whites into the chocolate mixture, lifting the mixture rather than stirring, to keep the mousse light and airy.

Spoon the mixture into 6 small glasses or ramekins, grate a little orange zest (be careful, it can be bitter) on top, and refrigerate for at least 3 hours before serving.

NOTE: Chocolate mousse should be eaten fairly soon after making, as it contains raw eggs that don’t keep for long.