In a medium saucepan over medium heat, combine 1 cup of freshly squeezed lemon juice, 1 cup of water, and ¾ cup of granulated sugar. Stir continuously until the sugar completely dissolves, about 3-5 minutes. Once fully dissolved, remove from heat and allow the syrup to cool completely in the saucepan.

In a large mixing bowl, pour in 1 cup of cold heavy whipping cream and add ½ cup of powdered sugar along with 1 teaspoon of pure vanilla extract. Using an electric mixer, whip the mixture on medium-high speed until soft peaks form, which should take about 3-5 minutes. In another bowl, beat 8 ounces of room temperature mascarpone cheese and the zest of one lemon until smooth. Gently fold the whipped cream into the mascarpone mixture until just combined.

Dip the ladyfinger cookies, one at a time, into the cooled lemon syrup for just a second. Layer half of the soaked ladyfingers in the bottom of the dish, then spread half of the prepared mascarpone cream over the top. Repeat with remaining ladyfingers, layering them once more followed by the rest of the cream.

Cover the assembled Lemon Tiramisu with plastic wrap or a lid and refrigerate for at least 4-6 hours, preferably overnight.

Before serving, garnish with extra lemon zest or candied lemon slices. Slice into squares and serve chilled.