Combine the milk, 4 1/2 ounces cream and 3/4 ounce of the sugar in a saucepan and bring to a boil.
In a bowl, whisk together the egg yolks and the remaining 3/4 ounce sugar, and then temper with the hot dairy mixture. Return the mixture to the heat; heat to 185 degrees F, stirring.
Pour the custard mixture over the chopped bittersweet chocolate and let sit for 1 minute. Add the gelatin sheets and whisk to combine into a ganache. Cool over an ice bath to 70 degrees F.
In 3 additions, fold the whipped cream into the cooled mousse mixture. Return to the ice bath and cool to a spreadable/pipeable consistency.
Pour the dark chocolate and white chocolate simultaneously into 24 half-sphere molds, or pour the white chocolate first and then the dark chocolate to create a marble effect. Refrigerate until set, 1 hour.
Pour the mousse into the chocolate cups and refrigerate until set, 1 hour.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.