In a medium saucepan, combine freshly squeezed lemon juice, water, and granulated sugar over medium heat. Stir until fully dissolved, about 2–3 minutes. Remove from heat and allow to cool completely, approximately 15 minutes.

In a mixing bowl, pour heavy whipping cream and add powdered sugar along with vanilla extract. Whip on medium speed until soft peaks form, about 2–4 minutes. In another bowl, beat mascarpone cheese with lemon zest until smooth. Gently fold whipped cream into mascarpone mixture.

Take a 9x9-inch dish, briefly dip ladyfinger cookies into cooled lemon syrup for 1–2 seconds. Arrange a layer of dipped ladyfingers at the bottom. Spread half of the mascarpone cream over the ladyfingers. Repeat with another layer of ladyfingers followed by remaining mascarpone cream.

Cover with plastic wrap and place in the refrigerator. Chill for at least 4–6 hours. Overnight chilling enhances flavor and texture.

When ready to serve, remove from refrigerator and garnish with extra lemon zest or candied lemon slices. Slice into squares and enjoy!