Bring the milk to a boil and pour it over the chopped chocolate in a mixing bowl. Add the egg yolk and stir until the mixture is smooth and glossy.

Beat the egg whites until stiff peaks form, then gradually add the sugar while continuing to beat.

Gently fold one-third of the beaten egg whites into the melted chocolate mixture, being careful not to deflate the whites.

Fold in the remaining egg whites until fully incorporated and the mixture is uniform.

Spoon the mousse into serving cups and chill for a few hours—if you can resist the temptation!

Serve with meringues and candied orange slices.