01 - Combine lemon juice and sugar in a small saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Remove from heat and let cool to room temperature, then stir in Limoncello liqueur. Set aside for assembly.
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, working rapidly to avoid oversaturation. Arrange a single layer of soaked ladyfingers in the bottom of a 9x9-inch dish, breaking pieces as needed to fit snugly.
04 - Spread half of the mascarpone cream evenly over the ladyfinger layer. Drop spoonfuls of half the lemon curd over the cream and gently swirl with a spatula to create marbled patterns.
05 - Repeat with another layer of dipped ladyfingers. Top with remaining mascarpone cream, spreading smoothly. Finish with remaining lemon curd, creating decorative swirls across the surface.
06 - Cover dish tightly with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld and texture to set properly.
07 - Just before serving, sprinkle fresh lemon zest over the top and arrange thin lemon slices decoratively across the surface. Slice into squares and serve chilled.