In a medium bowl combine graham cracker crumbs, 1/4 cup sugar and melted butter. Mix well and press into the bottom of a 9x13 inch pan.

In another medium bowl, whisk together sweetened condensed milk, lemon juice and lemon zest until smooth. Set aside.

With an electric mixer, beat whipping cream and 3 tablespoons sugar until stiff peeks form. Fold lemon juice mixture into whipped cream until smooth.

Pour over the prepared crust and freeze until firm, about 3 hours. Let stand at room temperature for about 5 minutes before slicing into bars and serving.