01 - Combine mascarpone cheese, lemon zest, lemon juice, sugar, and vanilla extract in a large mixing bowl. Beat with a hand mixer on medium speed until smooth and well combined.
02 - In a separate clean bowl, whip the heavy cream until stiff peaks form.
03 - Gently fold the whipped cream into the mascarpone mixture in two additions using a spatula, folding until fully incorporated and the mixture is light and airy.
04 - Spoon or pipe the mousse evenly into serving glasses or bowls, smoothing the tops as desired.
05 - Cover and refrigerate for at least 2 hours, or until completely set and thoroughly chilled.
06 - Top with fresh berries, a sprinkle of lemon zest, and mint leaves just before serving, if desired.