01 - Combine water, granulated sugar, lemon juice, and zest in a small saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Remove from heat and allow to cool to room temperature before using.
02 - In a chilled mixing bowl, beat cold heavy cream and powdered sugar with an electric mixer on high speed until stiff peaks form. Set aside.
03 - In a separate bowl, beat softened mascarpone cheese, vanilla extract, and lemon zest until completely smooth and creamy, ensuring no lumps remain.
04 - Gently fold the whipped cream into the mascarpone mixture using a spatula, mixing until fully incorporated and fluffy. Avoid overmixing to maintain airiness.
05 - Working quickly, dip each ladyfinger into the cooled lemon syrup for just 1-2 seconds per side. The cookies should be moistened but not saturated or falling apart.
06 - Arrange half of the dipped ladyfingers in a single tight layer in the bottom of a 9x9-inch dish. Break cookies as needed to fit evenly.
07 - Spread half of the mascarpone cream evenly over the ladyfinger layer using an offset spatula, ensuring complete coverage to the edges.
08 - Repeat dipping and arranging remaining ladyfingers over the cream. Top with remaining mascarpone cream, smoothing the surface completely.
09 - Cover dish tightly with plastic wrap and refrigerate for minimum 4 hours, preferably overnight, to allow flavors to develop and texture to set properly.
10 - Before serving, decorate top with fresh lemon slices and additional lemon zest if desired. Cut into squares and serve chilled.