Preheat the oven to 350°F (175°C). In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter. Mix until well combined.

Press the mixture firmly into the bottom of a 9x9 inch baking pan lined with parchment paper. Bake for 10 minutes, then remove and let cool.

In a small bowl, sprinkle gelatin over water and let it sit for 5 minutes to bloom.

In a large mixing bowl, whip the heavy cream until soft peaks form. In another bowl, combine limoncello, powdered sugar, lemon zest, and vanilla extract.

Heat the bloomed gelatin in the microwave for about 10 seconds until dissolved. Stir it into the limoncello mixture.

Gently fold the limoncello mixture into the whipped cream until fully incorporated.

Pour the filling over the cooled crust and spread evenly. Cover with plastic wrap and refrigerate for at least 2 hours or until set.

Once set, cut into bars and serve chilled. Enjoy!