01 - Beat the softened cream cheese with a hand mixer in a medium bowl until smooth and fluffy, about 2 minutes.
02 - Add granulated sugar, lemon zest, lemon juice, and vanilla extract to the cream cheese. Beat until well combined and creamy, scraping down sides as needed.
03 - In a separate clean bowl, whip the heavy cream and powdered sugar together with electric beaters until stiff peaks form, about 3-4 minutes.
04 - Gently fold the whipped cream into the lemon cheesecake mixture until nearly incorporated, then add sour cream and fold until fully blended and light.
05 - Spoon or pipe the mousse into individual serving glasses or bowls, filling each about three-quarters full.
06 - Cover containers with plastic wrap and refrigerate for at least 2 hours to allow mousse to set completely.
07 - Just before serving, top with extra lemon zest, fresh berries, and crushed graham crackers if desired.