Place the chopped white chocolate and butter in a heatproof bowl.
Melt the chocolate and butter gently over a double boiler, stirring until smooth.
Remove from the heat and allow the mixture to cool slightly.
In a separate bowl, whisk the egg yolks, sugar, and vanilla extract until smooth.
Gradually add the slightly cooled white chocolate mixture to the egg yolks while whisking continuously.
In another bowl, whip the heavy cream with the salt until soft peaks form.
Gently fold the whipped cream into the white chocolate mixture in batches.
Continue folding carefully until the mousse is smooth and airy.
Divide the mousse between six dessert glasses or ramekins.
Cover and refrigerate for at least 2 hours, or until set.
Garnish with fresh raspberries, white chocolate shavings, or mint leaves before serving.
Serve chilled and enjoy.