Begin by breaking the white chocolate into small pieces and placing them in a heatproof bowl. Set this bowl over a saucepan of simmering water, stirring until the chocolate melts completely.

In a separate small bowl, sprinkle the gelatin over cold water and let it sit undisturbed for about 5 minutes, then dissolve the gelatin in a small amount of boiling water.

In a clean mixing bowl, whisk the egg whites using an electric mixer until soft peaks form, about 3-5 minutes.

Slowly whisk the dissolved gelatin into the melted white chocolate until smooth.

Fold in the optional crème anglaise and the finely grated orange zest into the chocolate mixture gently with a spatula.

Gently fold the whipped egg whites into the chocolate mixture in three additions using a swirling motion.

Spoon the creamy mousse mixture into serving glasses, smoothing the tops for presentation.

Cover with plastic wrap and refrigerate for at least 4 hours, or overnight if possible.

Just before serving, prepare sweetened whipped cream and dollop it generously on top of each mousse.