With a rolling pin, crush graham crackers to make 1-1/2 C. Combine with sugar and melted butter. Press mixture evenly into 9" pie pan. Refrigerate for 1 hour. Separate egg, saving the whites for another use. Combine the yolks and one can of condensed milk. Beat well. Add gradually, while stirring, lime juice and the grated peel (zest) of lime. Stir until smooth and creamy. Pour into prepared crust and bake in a preheated 350 degree oven for 10 minutes.