In a small bowl, combine crushed Oreos and melted butter. Spoon about one tablespoon of crumb mixture into the bottom of 6-8 small dessert dishes (you may not use all the crumbs, depending on the size of your dishes).

Warm the hot fudge sauce in the microwave. Spoon 2 tablespoons of sauce over the crumb mixture in each dessert dish. Refrigerate while you prepare the mousse.

With an electric mixer, beat the cream cheese and peanut butter until smooth. Stir in the powdered sugar and beat until smooth.

In a separate bowl, beat the heavy cream until stiff peaks form. Gradually fold the whipped cream into the peanut butter mixture until smooth. Refrigerate the mousse for about 5-10 minutes.

Spoon or pipe the mousse over the hot fudge layer in the dessert dishes. Refrigerate at least 2 hours, or until firm. Garnish with chocolate shavings, if desired.