In a medium saucepan over low heat, combine fresh lemon juice, water, and granulated sugar, stirring until fully dissolved, about 3-5 minutes. Allow syrup to cool completely.

In a large mixing bowl, whip cold heavy whipping cream with powdered sugar and pure vanilla extract until soft peaks form, about 3-4 minutes. In another bowl, beat mascarpone cheese with lemon zest until smooth, then fold in whipped cream.

Dip each ladyfinger briefly in the cooled lemon syrup and arrange half in a 9x9-inch dish. Spread half of the mascarpone mixture over them. Repeat with remaining ladyfingers and cream.

Cover lemon tiramisu with plastic wrap and refrigerate for at least 4-6 hours, or overnight for best results.

Garnish with extra lemon zest or candied lemon slices before serving. Slice and enjoy!