Grate lemon zest from 1 lemon, set aside. Cut both lemons in half, squeeze to measure 7 Tablespoons of juice.
Mix evaporated and sweetend condensed milk in a small bowl. Add lemon juice, 1 Tablespoon at a time, stirring with a fork after each addition until well blended. Your mixture should be have a soft custard like consistancy. Stir in lemon zest.
Line the bottom of a 8x5x3 loaf pan with plastic wrap. Arrange 6 graham crackers on the bottom, carefully break/trim some for a snug fit.
Cover with 1 cup milk mixture, spreading to cover crackers. Repeat layers 2 times. Cover with remaining wafers.
Refrigerate overnight. Unmold onto plate just before serving. Spread top of dessert with cool whip.