01 - Combine water, lemon juice, and sugar in a small saucepan. Heat over medium-low, stirring until the sugar fully dissolves. Remove from heat and let cool completely before using.
02 - In a large mixing bowl, whisk cold mascarpone, heavy cream, sugar, lemon zest, lemon juice, and vanilla extract until smooth, thick, and slightly stiff.
03 - Briefly dip each ladyfinger into the cooled lemon syrup, just a quick pass on each side. Do not soak or the layers will become soggy.
04 - Arrange a single layer of dipped ladyfingers in the bottom of an 8x8-inch dish. Spread half of the lemon cream evenly over the top.
05 - Place a second layer of dipped ladyfingers over the cream. Top with the remaining lemon cream, smoothing the surface with a spatula.
06 - Cover tightly with plastic wrap and refrigerate for at least 4 hours, or overnight for the best texture and flavor.
07 - Before serving, finish with a sprinkle of fresh lemon zest and optional white chocolate curls or mint leaves. Serve well chilled.