1. Mix together the graham cracker crumbs and butter. Butter the sides and bottom of a 9-inch pie pan, and press the graham cracker mixture into sides and bottom of the pan.
2. In a mixing bowl, whisk together the 3 egg yolks, the condensed milk, lemon zest, lemon juice, and salt. Mix until smooth. In another bowl, beat the 3 egg whites with a handheld mixer until stiff. Gently fold the beaten whites into the lemon mixture. Pour into the prepared pie shell. Wrap well and freeze for at least 3 hours.
3. To serve, remove the pie from freezer, spread the whipped cream over the top, and let sit for 10 minutes before serving.
Recipe from My Family Table by John Besh/Andrews McMeel Publishing.