01 - Combine lemon juice and sugar in a small saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Remove from heat and allow to cool completely. Stir in limoncello and set aside.
02 - Beat cold heavy cream in a large bowl until soft peaks form. In a separate bowl, whisk together mascarpone cheese, powdered sugar, vanilla extract, and lemon zest until smooth and creamy. Gently fold the whipped cream into the mascarpone mixture until fully incorporated and no streaks remain.
03 - Quickly dip each ladyfinger into the cooled lemon syrup, ensuring a brief dip rather than soaking—this prevents the biscuits from becoming too soggy. Work efficiently to maintain texture.
04 - Arrange a single layer of dipped ladyfingers in the bottom of a 9x9-inch baking dish, breaking pieces as needed to fit. Spread half of the mascarpone cream evenly over the ladyfingers. Dollop half of the lemon curd in spoonfuls over the cream and gently swirl with a spatula to create a marbled effect.
05 - Create another layer with the remaining dipped ladyfingers. Top with the rest of the mascarpone cream, spreading smoothly. Finish by dolloping the remaining lemon curd over the surface and swirling gently.
06 - Cover the dish tightly with plastic wrap and refrigerate for a minimum of 4 hours, though overnight chilling is recommended for optimal flavor development and texture setting.
07 - Remove from refrigerator just before serving. Garnish generously with fresh lemon zest and arrange thin lemon slices on top if desired. Serve cold for the best texture and flavor experience.