01 - In a small saucepan, combine lemon juice and sugar. Heat over medium heat, stirring until sugar dissolves. Remove from heat, let cool, then stir in limoncello. Set aside.
02 - In a large bowl, beat the heavy cream until soft peaks form. In another bowl, whisk mascarpone, powdered sugar, vanilla, and lemon zest until smooth. Gently fold the whipped cream into the mascarpone mixture until fully combined.
03 - Quickly dip each ladyfinger into the cooled lemon syrup (do not soak). Arrange a layer of soaked ladyfingers in the bottom of a 9x9-inch dish. Spread half of the mascarpone cream over the ladyfingers. Dollop and gently swirl half of the lemon curd over the cream.
04 - Repeat with another layer of dipped ladyfingers, the rest of the mascarpone cream, and remaining lemon curd.
05 - Cover and refrigerate for at least 4 hours (preferably overnight) to allow flavors to meld and dessert to set.
06 - Before serving, garnish with lemon zest and thin lemon slices if desired.