In a medium saucepan over medium heat, combine freshly squeezed lemon juice, water, and granulated sugar, stirring until the sugar fully dissolves. Remove from heat and let it cool completely, about 30 minutes.

In a large bowl, whip the cold heavy cream using an electric mixer until soft peaks form, about 3–5 minutes. In another bowl, beat the room-temperature mascarpone cheese with lemon zest and powdered sugar until smooth. Gently fold the whipped cream into the mascarpone mixture.

Briefly dip each ladyfinger in the cooled lemon syrup and arrange a layer of dipped ladyfingers at the bottom of your dish. Spread half of the mascarpone cream over them. Repeat with another layer of ladyfingers and remaining cream.

Cover your completed Lemon Tiramisu with plastic wrap and refrigerate for at least 4–6 hours or ideally, overnight.

Before serving, garnish with extra lemon zest or candied lemon slices. Slice into squares or scoop into bowls.