Preheat the oven to 350 degrees F. Make the crust: In a mixing bowl, stir together the graham cracker crumbs, sugar and butter until fully combined. Press the mixture firmly into a 9-inch pie plate. Set aside.
Make the filling: In a medium bowl, mix the condensed milk, lemon juice, zest and egg yolks. Pour into the crust. Make the meringue: Beat the egg whites and cream of tartar in a medium bowl with an electric hand mixer until soft peaks form. Gradually beat in the sugar until stiff peaks form. Spread the meringue over the pie and seal the edge of the crust. Bake 15 to 20 minutes, or until the meringue browns slightly. (Be sure to watch the pie while it's baking. Meringue can burn quickly.) Let cool slightly on a rack, then chill in the refrigerator at least 2 hours before serving.