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 completely smooth and well combined.
02 - In a separate chilled bowl, whip the heavy cream using a hand mixer or stand mixer until stiff peaks form.
03 - Gently fold the whipped cream into the mascarpone mixture in two additions using a spatula. Fold until fully incorporated and the mixture becomes light and airy.
04 - Spoon or pipe the mousse evenly into individual serving glasses or bowls, smoothing the tops as desired.
05 - Cover the servings and refrigerate for at least 2 hours, or until the mousse is completely set and thoroughly chilled.
06 - Just before serving, top each portion with fresh berries, a sprinkle of fresh lemon zest, and mint leaves if desired.