Using a food processor, pulse the graham crackers until you have fine crumbs.
Add the graham cracker crumbs and sugar to a medium bowl and stir to combine. Mix in the melted butter and stir until it resembles wet sand.
Press the crust into a 9-inch pie dish and place it in the refrigerator.
In a large bowl, add the boiling water and gelatin powder. Stir until the gelatin completely dissolves.
Add the cold water and the ice cubes, and stir until the gelatin is slightly thickened. This step is important otherwise, the mixture won't set up if you add the cool whip before the gelatin has cooled and thickened a bit.
Add the whipped topping to the gelatin and then whisk together until smooth. Mix in lemon juice and lemon zest.
Pour the filling into the chilled crust and refrigerate for 6 hours or until the filling has set completely.
Top with lemon slices and zest before serving.
Updated on August 22, 2023Original Post on March 16, 2017