Break up or chop the chocolate into smaller chunks and place it in a bowl. Add a splash of cream and melt the chocolate, either in the microwave or using a double boiler. If using a microwave, heat the chocolate in 20 second bursts until melted, stirring between bursts. If using a double boiler, put the bowl atop a pot of lightly simmering water and stir until melted. Let the chocolate cool to room temperature.

Add the sugar to the heavy cream and whip it to stiff peaks. For best results, use a metal bowl. Do not use a plastic bowl.

Add the mascarpone to a large bowl. Pour in the chocolate and fold until mostly combined. Add half of the whipped cream and continue folding to lighten the mixture. Add the remaining whipped cream and any flavourants. For my version, I used the rind of two navel oranges. Fold until the mousse is uniform. Do not overmix or the cheese might become grainy. If this happens, mix in a splash of cream.

Transfer the mousse to the serving vessels of your choice and chill for a few hours in the fridge before serving.