Choose a 9x9-inch baking dish for assembly and set aside.

In a large mixing bowl, pour in chilled heavy cream and sprinkle granulated sugar over it. Beat on medium speed until soft peaks form.

In another bowl, combine mascarpone cheese, Limoncello liqueur, and vanilla extract. Beat until smooth and creamy, then fold in lemon zest.

Gently fold the whipped cream into the mascarpone mixture to maintain a light, airy consistency.

Mix equal parts of Limoncello and water in a shallow dish. Quickly dip each ladyfinger into the soaking liquid.

Arrange half of the soaked ladyfingers in a single layer in the baking dish and spread half of the mascarpone mixture over them. Repeat with remaining ingredients.

Cover and refrigerate for at least 4 hours, preferably overnight for best flavor integration.

Dust the top with cocoa powder or lemon zest before serving. Cut into squares and serve chilled.