Heat the cream in a heavy saucepan over medium-high heat until it's very hot but not yet boiling. Add the white chocolate and stir continually until melted. Remove from heat. Note: The mixture may look a little yellow but it will whiten as it cools. Pour the mixture into a large bowl and cover with plastic wrap. Refrigerate overnight.
Once thoroughly chilled, beat the mixture with an electric mixer until it begins to stiffen. Add the powdered sugar and continue beating until stiff peaks form. For a pretty presentation, pipe the mousse into the stemware or pastry cups. For a fancier look, sprinkle with edible glitter.
Refrigerate the mousse until ready to serve. Can be made well in advance.