In a small saucepan over medium heat, combine ½ cup freshly squeezed lemon juice, ¼ cup water, and ⅓ cup granulated sugar. Stir continuously until the sugar is fully dissolved, about 3–5 minutes. Once dissolved, remove from heat and let the syrup cool completely.

In a chilled mixing bowl, whip 1 cup of cold heavy whipping cream with 3 tablespoons of powdered sugar and 1 teaspoon of pure vanilla extract until soft peaks form, which should take about 3–4 minutes. In another bowl, beat 1 cup of room-temperature mascarpone cheese with 1 tablespoon of lemon zest until smooth. Gently fold the whipped cream into the mascarpone mixture.

Take a shallow dish and briefly dip half of the ladyfinger cookies into the cooled lemon syrup, then layer these dipped ladyfingers at the bottom of the dish, followed by half of the mascarpone cream.

Repeat the layering with the remaining ladyfingers and mascarpone cream, smoothing the top for an even finish.

Cover the assembled lemon tiramisu with plastic wrap and refrigerate for 4–6 hours, or ideally overnight.

Before serving, garnish the top of the lemon tiramisu with extra lemon zest or candied lemon slices.