Let cream cheese sit at room temperature until softened.
Beat softened cream cheese with granulated sugar until smooth and fluffy.
Add lemon juice, lemon zest, and vanilla extract. Beat to incorporate.
In a chilled bowl, whip heavy cream to stiff peaks.
Gently fold whipped cream into the lemon cream cheese mixture until fully combined.
Spoon or pipe mousse into clear serving glasses or ramekins.
Chill for at least 2 hours before serving.
Top with optional garnishes like whipped cream, lemon twists, mint, or graham cracker crumbs.