Prepare the Lemon Syrup: In a small saucepan, combine water and granulated sugar. Heat over medium heat, stirring until the sugar dissolves. Remove from heat and stir in the fresh lemon juice. Set aside to cool.

Make the Mascarpone Filling: In a large mixing bowl, beat the cold mascarpone cheese until smooth. In a separate cold bowl, beat the cold heavy cream with the powdered sugar until stiff peaks form. Gently fold the whipped cream into the smooth mascarpone cheese. Stir in the lemon zest and vanilla extract (if using) until just combined.

Assemble the Tiramisu: Lightly dip each ladyfinger into the cooled lemon syrup for just a few seconds on each side (don't soak them). Arrange a layer of the soaked ladyfingers in the bottom of your baking dish.

Spread half of the mascarpone mixture evenly over the ladyfinger layer.

Arrange another layer of lemon-soaked ladyfingers over the mascarpone mixture.

Spread the remaining mascarpone mixture evenly over the second layer of ladyfingers.

Chill: Cover the dish with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the flavors to meld and the tiramisu to set.

Serve: Before serving, garnish with extra lemon zest or a light dusting of powdered sugar, if desired. Slice and enjoy this refreshing Lemon Tiramisu!