Put milk in 9-inch pan in freezer for 45 minutes to 1 hour to thicken and freeze a little. Take out and beat in bowl with 1 cup sugar, lemon rind and lemon juice; beat until stiff peaks form.
Sprinkle most of crumbs on bottom of 8-inch pan; add filling and sprinkle the rest of graham cracker crumbs on top. Put in freezer overnight!