Set a heatproof bowl over a pot of barely simmering water (double boiler method). Add the chopped white chocolate and stir gently until smooth and completely melted. Remove from heat and let it cool slightly.
Prepare 1 cup of your favorite brewed coffee and let it cool to room temperature.
In a chilled mixing bowl, whip the heavy cream until soft peaks form. Set aside in the fridge to keep cold.
In a separate clean bowl, beat the egg whites until frothy. Gradually add the granulated sugar and continue beating until stiff peaks form.
Gently stir the cooled coffee and vanilla extract into the melted white chocolate until fully combined.
Carefully fold the whipped cream into the white chocolate and coffee blend using gentle motions with a spatula to keep the mixture airy.
Fold in the beaten egg whites in two additions to keep the mousse fluffy and smooth.
Spoon or pipe the mousse into individual cups or bowls. Refrigerate for at least 3 hours until set.
Just before serving, sprinkle chocolate shavings on top. Optionally add a dusting of cocoa powder or a few coffee beans.