01 - Combine water, granulated sugar, lemon juice, and zest in a small saucepan. Heat over medium heat, stirring continuously until sugar completely dissolves. Remove from heat and allow to cool completely before using.
02 - In a chilled mixing bowl, beat heavy cream and powdered sugar with an electric mixer on high speed until stiff peaks form. Set aside.
03 - In a separate bowl, gently beat mascarpone cheese, vanilla extract, and lemon zest until smooth and creamy, taking care not to overmix.
04 - Gently fold the whipped cream into the mascarpone mixture using a spatula. Fold until fully incorporated and mixture is light and fluffy.
05 - Working quickly, dip each ladyfinger into the cooled lemon syrup. Ensure each cookie is moistened but not saturated or soggy. Dip just before placing to prevent excessive softening.
06 - Arrange half of the dipped ladyfingers in a single layer in the bottom of a 9x9-inch dish. Spread half of the mascarpone cream evenly over the ladyfingers using an offset spatula.
07 - Repeat with remaining ladyfingers and mascarpone cream. Smooth the top surface evenly with spatula. Cover tightly with plastic wrap.
08 - Refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld and texture to set properly.
09 - Before serving, garnish with fresh lemon slices and additional lemon zest if desired. Serve chilled.