In a small saucepan, combine 1 cup of fresh lemon juice, 1/2 cup of water, and 1/2 cup of granulated sugar. Heat over medium-low until the sugar dissolves completely, stirring occasionally—this should take about 5 minutes. Once dissolved, remove from the heat and let the syrup cool completely to room temperature.

In a large mixing bowl, pour 1 cup of very cold heavy whipping cream. Using an electric mixer, whip the cream at medium-high speed for about 2-3 minutes, then gradually add 1/4 cup of powdered sugar and 1 teaspoon of pure vanilla extract. Continue whipping until soft peaks form.

In another bowl, beat together 1 cup of mascarpone cheese and the zest of 2 lemons until smooth and creamy. Use a spatula to gently fold in the whipped cream from the previous step.

Take the cooled lemon syrup and dip each ladyfinger into it for no more than 1-2 seconds to soak. Arrange a single layer of these lemon-soaked ladyfingers in the bottom of a 9x9-inch dish. Spread half of your mascarpone mixture evenly over the ladyfingers.

Repeat this process to form another layer of dipped ladyfingers followed by the remaining mascarpone mixture on top.

Cover the dish with plastic wrap or a lid and refrigerate for at least 4-6 hours, preferably overnight. This chilling time is crucial for the flavors to meld.

When you're ready to serve, garnish the top with extra lemon zest or candied lemon slices. Slice into squares and serve chilled.