Mix together the cracker crumbs and melted butter. Press the mixture firmly into a 9" pie plate. Chill in the freezer while preparing the filling.
Using an electric mixer, beat the whipping cream until stiff peaks form. Set aside.
Using the same mixer, beat together the cream cheese and sugar.
Mix in the condensed milk, key lime juice, and lime zest. Add in the whipped cream and mix again until smooth.
Pour over prepared crust and smooth the surface. Chill uncovered in the refrigerator for a minimum of 6 hours or best to let it set overnight.
Garnish with some more whipped cream and key lime slices if desired.