2 cans Pet evaporated milk, chilled until very cold

Whip milk at high speed until thick. Slowly add 1 1/2 cups sugar and beat until thick. Squeeze juice from 3 lemons and grate rind from 1 1/2 lemons. Fold into milk mixture. Sprinkle graham cracker crumbs in 9 x 13 inch pan. (Crumbs should cover bottom of pan.) Pour in milk mixture. Sprinkle top with crumbs. Freeze overnight. (Store in freezer until ready to use.)