In a mixing bowl, whisk together the heavy cream, limoncello, sugar, vanilla extract, and lemon zest until soft peaks form.

In another bowl, beat the egg whites until stiff peaks form.

Gently fold the egg whites into the limoncello mixture until fully combined.

Spoon the mousse into serving glasses and refrigerate for at least 2 hours to set.

Once set, garnish each mousse with lemon zest and a mint leaf before serving.