Place chocolate and heavy cream in a microwave safe bowl, then microwave in 30 second intervals until the chocolate has completely melted. Whisk together until well mixed. Set aside to cool.
Place heavy cream in the bowl of a stand mixer fitted with whisk attachment, then whisk on medium speed until stiff peaks form. Transfer whipped cream to a small bowl.
Place cream cheese, peanut butter, confectioner’s sugar, and Kosher salt in the same stand mixer bowl fitted with the whisk attachment. Whisk until very smooth and creamy. Use a rubber spatula to stir in half of the whipped cream.
Spoon some of the ganache into cups, then divide the peanut butter mousse between them, smoothing the tops with a spatula. Place a dollop of the remaining whipped cream on top.
Allow the mousse cups to chill in a fridge for at least 1 hour, then serve with chocolate shavings, crushed cookies, chopped peanut butter cups, or chopped peanuts (if wanted).