Prepare Lemon Syrup: In a small saucepan, combine fresh lemon juice and granulated sugar over medium heat. Stir gently until the sugar dissolves, about 3–5 minutes. Remove from heat and mix in limoncello and extra lemon zest. Allow syrup to cool.

Make the Mascarpone Cream: Beat mascarpone cheese until smooth. In a separate bowl, whip heavy cream, powdered sugar, and vanilla extract until soft peaks form. Fold into mascarpone with a pinch of salt.

Assemble Tiramisu: Dip ladyfingers quickly in the cooled lemon syrup. Layer dipped ladyfingers in dish, spread half of the mascarpone cream mixture, then repeat layers.

Chill and Serve: Cover with plastic wrap and refrigerate for at least 4 hours or overnight. Garnish with lemon zest, lemon slices, and mint leaves before serving.