In a saucepan over medium heat, combine freshly squeezed lemon juice, water, and granulated sugar. Stir the mixture until the sugar dissolves completely, which should take around 2-3 minutes. Once dissolved, remove it from heat and let it cool completely at room temperature.

In a large mixing bowl, whip cold heavy whipping cream with powdered sugar and a splash of vanilla extract until soft peaks form, taking about 4-5 minutes with an electric mixer on high speed. In a separate bowl, beat the mascarpone cheese and freshly grated lemon zest until smooth and creamy. Gently fold the whipped cream into the mascarpone mixture until thoroughly combined.

Take the cooled lemon syrup and briefly dip each ladyfinger into it, ensuring they soak just enough without becoming soggy. Lay the dipped ladyfingers in a 9x9-inch dish in a single layer. Spread half of the zesty mascarpone cream over the ladyfingers evenly, then repeat the layering process with another set of dipped ladyfingers followed by the remaining cream.

Cover the assembled Lemon Tiramisu with plastic wrap or a lid and place it in the refrigerator. Allow it to chill for at least 4-6 hours, but preferably overnight.

Once chilled, remove the Lemon Tiramisu from the refrigerator. Before serving, garnish with a sprinkle of fresh lemon zest, a few mint leaves, or some candied lemon slices for an extra touch of elegance. Cut into squares and serve.