In a medium saucepan, combine 1 cup of water and ½ cup of granulated sugar over medium-high heat. Stir continuously until the sugar is fully dissolved, about 3-5 minutes. Remove from heat and stir in ½ cup of limoncello and juice of 1 lemon. Set aside to cool.

In a large mixing bowl, whip 1 cup of mascarpone cheese on low speed until loosened, about 1 minute. Gradually mix in ½ cup of lemon curd, ¼ cup of limoncello, and juice of another lemon until just combined.

In a separate bowl, whisk 1 cup of heavy whipping cream and ½ cup of powdered sugar until stiff peaks form. Fold ⅓ of whipped cream into mascarpone mixture, then gently incorporate remaining cream.

Quickly dip ladyfingers into cooled limoncello syrup for about 2 seconds on each side. Arrange a layer of dipped ladyfingers in a 9x13 pan, spread half of the mascarpone mixture over, then add another layer of ladyfingers followed by remaining mascarpone cream.

Cover tightly with plastic wrap and refrigerate for at least 4 hours, preferably overnight.

Before serving, whip additional heavy cream with 2 tablespoons of powdered sugar until stiff peaks form. Pipe over the tiramisu and sprinkle with fresh lemon zest.