This classic chocolate mousse recipe is courtesy of Clare Vivier and her French journalist husband, Thierry. Lots of well-beaten egg whites make this chocolate mousse especially airy.
Melt chocolate and butter in a large heatproof bowl set over (not in) a pot of simmering water, stirring occasionally, until completely smooth. Remove from heat and let cool 5 minutes. Add yolks, one at a time, stirring until fully incorporated.
Beat egg whites and a pinch of salt on medium speed in a mixer fitted with the whisk attachment until frothy, 1 minute. Increase speed to medium-high and continue beating whites until soft peaks form. Add sugar, 1 tablespoon at a time, until mixture is thick and glossy and stiff peaks form, 3 minutes.
Gently stir one-third of egg whites into chocolate mixture to incorporate. Fold in remaining egg whites in two additions, being careful not to overmix. Transfer mousse to a large serving bowl; refrigerate at least 4 hours and up to 1 day. Serve, with whipped cream and fruit.
Food-safety note: The eggs in this recipe are not cooked.