Stir the crushed vanilla wafers and melted butter together until everything looks evenly coated. Press the mixture firmly into a pie dish, working it up the sides a bit too. Pop it in the fridge to chill while you make the filling.
Sprinkle the gelatin over the cold water and let it sit for about five minutes so it can soften.
In a saucepan, whisk together the egg yolks, sugar, lemon juice, and zest. Cook over medium heat, stirring constantly, until the mixture thickens and looks smooth and glossy.
Remove the pan from the heat and stir in the softened gelatin until it completely dissolves. Let the mixture cool to room temperature.
In a separate bowl, beat the egg whites until stiff peaks form. Gently fold them into the cooled lemon mixture, followed by the whipped cream. Take your time here to keep that light, fluffy texture.
Pour the filling into the chilled crust, smooth the top, and refrigerate for at least four hours until fully set.