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 completely before using.
02 - In a chilled mixing bowl, beat heavy cream and powdered sugar with electric mixer on high speed until stiff peaks form. Set aside.
03 - In separate bowl, whisk mascarpone cheese, vanilla extract, and lemon zest until completely smooth and no lumps remain.
04 - Gently fold whipped cream into mascarpone mixture using spatula. Continue folding until fully incorporated and mixture is light and fluffy. Avoid overmixing.
05 - Working quickly, dip each ladyfinger into cooled lemon syrup for 1-2 seconds per side. Ladyfingers should be moist but not saturated or falling apart.
06 - Arrange half of dipped ladyfingers in single layer in 9x9-inch baking dish. Spread half of mascarpone cream evenly over ladyfingers using offset spatula.
07 - Repeat with remaining ladyfingers and remaining mascarpone cream. Smooth top surface evenly with spatula.
08 - Cover dish tightly with plastic wrap. Refrigerate for minimum 4 hours or preferably overnight to allow flavors to develop and texture to set properly.
09 - Remove from refrigerator just before serving. Garnish with fresh lemon slices and additional zest if desired. Cut into squares and serve cold.