1. In a saucepan, heat the cream over very low heat. Add the white chocolate pieces and mix until the mixture is smooth.
2. Remove the saucepan from the heat, let it cool, and add the orange essence. Refrigerate for 2 hours.
3. Break the dark chocolate into small pieces in a bowl. Melt it in a double boiler and set it aside off the heat.
4. Separate the egg whites from the yolks and beat the whites until stiff. Leave them on hold.
5. Add the egg yolks to the melted chocolate mixture, whisking. Gently incorporate the beaten egg whites into the melted chocolate mixture.
6. Divide the mousse into small cups or individual bowls. Decorate with physalis and serve very fresh.