Preheat the oven to 350ºF and adjust the rack to the middle position. Place the graham crackers in the bowl of a food processor. Pulse until finely ground. Add the butter and process until moistened. Pour the crumb mixture into an 8×8 pan and press evenly to form a crust. Bake for 11 minutes. Cool completely.
Pour the lemon juice and water into medium-size saucepan. Sprinkle the gelatin on the surface of the lemon juice. Heat the gelatin-juice mixture over medium-low heat until the gelatin is dissolved, about 5-7 minutes. Remove from the heat and add the sugar, stirring until the sugar is completely dissolved. Cool until slightly thickened.
Beat the heavy cream until fluffy.
In a separate bowl, beat cream cheese, sugar and lemon juice and lemon zest with mixer until smooth. Mix in the gelatin mixture until combined. Gently fold in the whipped cream.
Pour the filing over the crust and using an offset spatula, spread evenly. Cover with plastic wrap and chill for at least 3 hours and up to overnight. Serve cold.
