DO FILLING. Whip butter and margarine until smooth. Add in powdered sugar and vanilla extract. Beat until creamy and well blended. Stir in chopped cashew nuts.
ASSEMBLE. Lay a piece of plastic wrap (about 12 x 11 inches) on the working area. Spread about 1/4 cup chopped cashew nuts evenly on top of plastic wrap. Spread thick layer of butter cream on top of 3 whole Graham crackers. Arrange and lay the crackers, butter cream facing down, side by side over the nuts. Repeat 2 times to make 3 layers.
COVER the top and sides with a thick layer of butter cream. Leave about 1/3 cup of butter cream for decoration. Cover with plastic wrap to hold.
CHILL for 30 minutes. Turn loaf over and unwrap. Serve.