In a medium bowl, combine the softened cream cheese, powdered sugar, vanilla extract, lemon juice, and salt. Beat with a hand mixer until smooth and creamy.

In a separate bowl, whip the heavy cream until stiff peaks form.

Gently fold the whipped cream into the cream cheese mixture until fully combined.

In a blender or food processor, puree the fresh blackberries until smooth. If desired, strain the puree to remove seeds.

Fold the blackberry puree into the cheesecake mixture until evenly mixed, creating a marbled effect.

Spoon the mousse into serving cups or bowls and refrigerate for at least 2 hours to set.

Before serving, garnish with fresh blackberries and mint leaves if desired.