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Next, the egg whites need to be whipped to perfection. Using room-temperature egg whites will yield the best results, allowing them to increase in volume and form soft peaks. Incorporate sugar into the egg whites gradually; this strengthens their structure and helps achieve that desirable meringue effect.
The key to incorporating the egg whites into the chocolate mixture lies in a gentle folding technique. Using a thin-edged metal spoon, fold in a third of the egg whites to lighten the mixture before gradually combining the rest. This step is vital to maintaining the airy texture that characterizes a good mousse.