01 - Combine water, granulated sugar, lemon juice, and lemon zest in a small saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Remove from heat and allow syrup to cool completely 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, incorporating until fully combined and fluffy. Do not overmix to maintain light texture.
05 - Working quickly, dip each ladyfinger into cooled lemon syrup for just 1-2 seconds per side. Ladyfingers should be moistened but not soggy or falling apart.
06 - Arrange half of dipped ladyfingers in a single layer in the bottom of a 9x9-inch dish. Spread half of mascarpone cream evenly over ladyfingers, smoothing top with spatula.
07 - Repeat dipping process with remaining ladyfingers and arrange in second layer. Spread remaining mascarpone cream over top, creating smooth, even surface.
08 - Cover dish tightly with plastic wrap and refrigerate for minimum 4 hours, preferably overnight, to allow flavors to meld and dessert to set completely.
09 - Just before serving, garnish top with fresh lemon slices and additional lemon zest if desired. Cut into squares and serve chilled.