Makes an 8x8 or 6x10 pan (8-9 servings). For a 9x13 pan, double the ingredients.
3/4 cup graham cracker crumbs (5 whole crackers)
7 tablespoons butter, divided
2 tablespoons sugar
Additional 1/2 cup sugar
1 quart vanilla ice cream, softened
1 pint lime sherbet, softened
1 egg, lightly beaten
2 tablespoons lemon juice
Remove ice cream and lime sherbet from freezer and allow to sit at room temperature for about 1/2 hour to soften. Meanwhile, combine the graham cracker crumbs, 3-1/2 tablespoons butter and 2 tablespoons sugar. Press into an ungreased 8x8 or 6x10 pan. Freeze until firm.
Combine softened ice cream and sherbet in large mixing bowl. Pour over crust. Freeze until firm.
In a heavy saucepan, combine egg and remaining 1/2 cup sugar. Stir in lemon juice and remaining 3-1/2 tablespoons butter. Cook and stir until mixture reaches about 160 degrees and coats the back of a metal spoon. Cover and refrigerate until cool.
Spread over ice cream mixture. Cover and freeze for 3 hours or overnight. May be frozen for up to 2 months. Just before serving, remove from the freezer and cut into squares.