Cut a piece of foil into 12x3-in. rectangle. Line the bottom of a 5-3/4x3x2-in. loaf pan with foil, so that the foil comes up over the ends of the pan. Combine wafer crumbs and melted butter; press onto bottom of prepared pan. Spoon ice cream over crumbs; smooth with a spatula. Sprinkle with nuts. Freeze until firm.
In a small saucepan, combine the remaining ingredients; bring to a boil over medium heat. Reduce heat to simmer. Cook and stir for 4 minutes or until thickened. Refrigerate mixture until completely cool, stirring occasionally. Spread over ice cream. Cover and freeze until firm. Remove from refrigerator 10-15 minutes before serving.