Add the graham crackers, sugar, and a pinch of salt to a food processor. Blend until uniform crumbs form, then add melted butter and continue to mix until the mixture sembles wet sand.
Press the crust mixture into a 9-inch springform pan. Firmly press along the sides and bottom of the pan, then place into the refrigerator to set.
In a large bowl, add cream cheese and mix on low speed for about 30 seconds, until smooth. Then add sweetened condensed milk, and lemon zest. Mix with a hand mixer on medium speed until combined, about 1 minute.
In a separate medium bowl, add heavy cream beat until stiff peaks (it should look like whipped cream).
Fold the whipped cream into the cream cheese mixture, then add in lemon juice, lemon extract, and a tiny pinch of salt. Whisk together with. a hand whisk until just combined and smooth. Pour into the graham cracker crust and place into the refrigerator for 8 hours, overnight. (if storing longer, cover with plastic wrap)
Just before serving, make the lemon whipped cream. Combine cold heavy cream and powdered sugar in a bowl. Use an electric mixer to mix until stiff peaks form. Then add the lemon juice and lemon zest and mix until just combined. Add on top of the lemon ice box pie and serve.
Notes
To save time, use a store-bought graham cracker crust and just make the filling.
This pie is best served cold, fresh out of the fridge. Avoid leaving in the summer sun.
Gently fold in the whipped cream when mixing everything together for the filling. It's important not to overmix the whipped cream and cream cheese as the mixture can break down and become runny and not set properly.
When making the graham cracker crust, press it firmly into the pan. It helps to use the bottom of a glass or bottom of a measuring cup to compact it. Chill in the fridge to set.