01 - Combine water, granulated sugar, and lemon zest in a small saucepan. Bring to a simmer while stirring until sugar completely dissolves. Remove from heat, stir in limoncello, and allow to cool completely.
02 - In a large bowl, whip cold heavy cream with powdered sugar using an electric mixer or hand whisk until stiff peaks form.
03 - In a separate bowl, combine softened mascarpone, lemon zest, fresh lemon juice, and vanilla extract. Mix until smooth and well incorporated.
04 - Gently fold the whipped cream into the mascarpone mixture until fully combined and smooth. Avoid overmixing to maintain light texture.
05 - Quickly dip 12 ladyfingers, one at a time, into the cooled lemon syrup. Do not oversoak as they will become soggy. Arrange in a single layer in a 9x9-inch dish.
06 - Spread half of the lemon mascarpone cream evenly over the ladyfingers using a spatula, ensuring complete coverage.
07 - Repeat the dipping process with remaining ladyfingers and arrange as second layer. Top with remaining mascarpone cream, spreading smoothly.
08 - Cover dish with plastic wrap and refrigerate for at least 4 hours or overnight. This allows flavors to meld and texture to set properly.
09 - Before serving, garnish with fresh lemon slices and mint sprigs if desired. Slice and serve chilled.