01 - Combine water, sugar, and lemon zest in a small saucepan. Bring to a simmer over medium heat, stirring until sugar completely dissolves. Remove from heat, stir in lemon juice, and allow to cool completely before using.
02 - Beat heavy cream with powdered sugar and vanilla in a large bowl until soft peaks form. In a separate bowl, gently mix mascarpone with lemon zest until smooth. Fold whipped cream into mascarpone mixture until fully combined and fluffy.
03 - Quickly dip each ladyfinger into cooled lemon syrup, ensuring just a brief dip rather than soaking. Arrange dipped ladyfingers in a single layer covering the bottom of a 9x9-inch baking dish.
04 - Spread half the mascarpone mixture evenly over the ladyfingers layer. Smooth surface with a spatula to ensure uniform coverage.
05 - Add another layer of dipped ladyfingers over the cream, then top with remaining mascarpone mixture. Smooth the top surface evenly with spatula.
06 - Cover dish with plastic wrap and refrigerate for minimum 4 hours, preferably overnight, to allow flavors to meld and texture to set properly.
07 - Decorate with thin lemon slices and fresh mint leaves just before serving. Slice and serve chilled.