In a heatproof bowl, combine white chocolate and water. Set over a pot of simmering water, stirring occasionally until melted and smooth. Remove from heat and let cool.

In a mixing bowl, whip the heavy cream (1 1/2 cups) with vanilla extract until soft peaks form. Set aside.

In another bowl, beat the egg whites until stiff peaks form. Gently fold the cooled chocolate mixture into the whipped cream.

Carefully fold the egg whites into the chocolate cream mixture until evenly combined.

Spoon the mousse into serving dishes and chill for at least 2 hours or until set. Serve chilled, topped with extra whipped cream if desired.