In a medium mixing bowl, beat the peanut butter, softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy. Set aside.
In a separate bowl, beat the cold heavy whipping cream until stiff peaks form. This step is key to getting a light and airy mousse texture.
Gently fold the whipped cream into the peanut butter mixture in batches. Use a spatula to combine without deflating the whipped cream. Mix just until fully incorporated and smooth.
Spoon the mousse into serving glasses or bowls. Refrigerate for at least 1 hour to set. Before serving, top with optional toppings like whipped cream, chocolate drizzle, or crushed nuts.