Two days before you plan to serve the dessert, in a small saucepan, heat the cream over medium heat just until it boils. Immediately turn off the heat. Place the chocolate in a medium bowl. Pour the hot cream over the chocolate and whisk until melted and smooth. Strain into another bowl, cover, and refrigerate overnight.
The next day, remove the mixture from the refrigerator and, using a mixer fitted with a whisk attachment or a hand mixer, whip it into fluffy, soft peaks. Return to the refrigerator.
In a clean dry bowl, whip the egg whites until soft peaks form, then add the sugar and continue whipping until glossy and stiff, about 30 seconds more. Fold into the white chocolate mixture, and then spoon the mixture (or pipe through a pastry bag) into glasses or chocolate bags.
Melt chocolate over hot water. Using a thin small clear 4-sided cellophane bag cut the top off to desired height. Un-crease the bag so it stands up and open. Using a paintbrush, coat the inside of the bag well with chocolate. Put in the freezer to set up until very hard, about 30 minutes. Cut the bag a little and pull it away from the chocolate. Store chilled until ready to serve. To serve, fill it with white chocolate mousse then lay it on a plate on its side so it looks like it's spilling over. Garnish it with a cascade of mixed berries and a mint sprig. You can fill it with truffles, too.
Notes about the recipe: Ganache is a word that we've been seeing on more and more dessert menus. It has a rich, fancy, very French sound, but ganache is essentially just a combination of chocolate and water or cream. Depending on the proportions, the mixture can be used in a variety of ways: as a glaze, a filling, or a candy center, to name just the ways we use it in this book. With enough cream added, it becomes whip-able, and that's the foundation of this white-chocolate mousse. White chocolate is devastatingly popular, but it's also not exactly chocolate. It's mostly cocoa butter, extracted from cocoa beans and enhanced with sugar and vanilla. White chocolate is not the same thing as the "confectionery coating" or "white coating" you see in the market; real white chocolate contains cocoa butter. Note that you'll need two days for making this dessert.