Dark chocolate orange mousse

Instructions

1. Using a hand-held electric whisk, beat the egg whites and sugar together on a low speed until the sugar has dissolved. Increase the speed and beat, scraping down the sides, until stiff peaks form – this should take about 10 minutes.
2. Put chocolate bars in a medium heatproof bowl and pour over 80ml boiling water from the kettle. Let stand for 30 seconds, then stir until the chocolate is melted and the mixture is smooth. Set the bowl of melted chocolate over a large bowl filled with ice water and whisk for 2-3 minutes, or until thickened slightly.
3. Remove the bowl of whipped chocolate from the bowl of ice water, then fold in the Greek yogurt, orange zest and a large spoonful of the beaten egg whites. Fold in the remaining egg whites until just combined.
4. Divide the chocolate-orange mousse between 4 small dessert glasses, then chill in the fridge for 2 hours, or until set. Scatter over the chopped pistachios just before serving.