01 - In a small saucepan, combine water, sugar, and lemon zest. Bring to a simmer over medium heat, stirring until sugar dissolves. Remove from heat, stir in lemon juice, and let cool completely.
02 - In a large bowl, beat the heavy cream with powdered sugar and vanilla until soft peaks form. In a separate bowl, gently mix the mascarpone with lemon zest until smooth. Fold the whipped cream into the mascarpone until fully combined and fluffy.
03 - Quickly dip each ladyfinger into the cooled lemon syrup (do not soak; just a quick dip). Arrange a layer of dipped ladyfingers in the bottom of a 9x9-inch dish.
04 - Spread half the mascarpone mixture over the ladyfingers and smooth with a spatula.
05 - Add another layer of dipped ladyfingers, followed by the remaining mascarpone mixture. Smooth the top.
06 - Cover and refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld.
07 - Garnish with lemon slices and fresh mint before serving, if desired.