Combine graham cracker crumbs, sugar, and melted butter. Press into the bottom of a 9x13 inch baking dish.
In a separate bowl, whip heavy cream until soft peaks form. Gradually add sweetened condensed milk, lemon juice, and lemon zest, mixing until combined.
Pour the lemon mixture over the graham cracker crust. Refrigerate for at least 4 hours, or overnight.
Notes
For a more intense lemon flavor, add an extra tablespoon of lemon zest.