In a large bowl, whip the heavy cream until soft peaks form. Gradually add the powdered sugar and continue whipping until stiff peaks form.
In a separate bowl, whisk together the peanut butter, vanilla extract, and salt until smooth.
Gently fold about one-third of the whipped cream into the peanut butter mixture to lighten it. Then, carefully fold the peanut butter mixture into the remaining whipped cream until just combined. Be careful not to overmix.
Spoon the mousse into individual serving dishes or glasses.
Chill for at least 30 minutes before serving. Garnish with chopped peanuts or chocolate shavings if desired.
Notes
This mousse is best served chilled. You can make it a day in advance and store it covered in the refrigerator.