In a small saucepan, combine the water and granulated sugar. Stir over medium-high heat until the sugar is completely dissolved. Once dissolved, remove the saucepan from heat and stir in the limoncello and freshly squeezed lemon juice. Transfer the syrup to a shallow dish and allow it to cool slightly before using.

Using a large mixing bowl or the bowl of a stand mixer, begin by beating the chilled mascarpone cheese on medium-low speed for about 30 seconds, just until it softens. Add the prepared lemon curd to the bowl and mix until fully incorporated. Then pour in the limoncello and lemon juice, mixing gently until smooth—avoid overmixing to prevent the mascarpone from becoming grainy. Set the mixture aside.

In a separate large bowl (or the clean bowl of a stand mixer), whip the heavy cream with the granulated sugar until stiff peaks form. Add about one-third of the whipped cream into the mascarpone mixture and stir it in to lighten the texture. Gently fold the remaining whipped cream into the mascarpone mixture until fully combined and smooth.

Take each ladyfinger and briefly dip one side into the cooled limoncello syrup for approximately 2 seconds, then flip and dip the other side for another 2 seconds. Do not soak them too long; they should remain slightly crisp to avoid sogginess in the finished dessert.

Line the dipped ladyfingers in a single layer along the bottom of a 9x13-inch dish, positioning them in the same direction. Trim the cookies as needed to fit the pan.

Spoon and spread half of the mascarpone-cream mixture evenly over the layer of ladyfingers. Dip and arrange the second layer of ladyfingers the same way, and top with the remaining mascarpone mixture, spreading it evenly and smoothing out the surface.

Cover the dish tightly with plastic wrap or foil and refrigerate for a minimum of 4 hours, though overnight chilling is ideal for the best texture and flavor. Add whipped cream topping just before serving, if desired.

In a large bowl, whip the heavy cream with 2 to 3 tablespoons of powdered sugar, adjusting for your preferred level of sweetness, until stiff peaks form. Transfer the whipped cream to a piping bag fitted with a round tip or a zip-top bag with one corner snipped off. Pipe neat dollops in rows across the top of the tiramisu, then finish by sprinkling with fresh lemon zest.