NB. Use the finest grain powdered sugar for this recipe and graham cracker crumbs should be ground to a fine powder Cream margarine, peanut butter & sugar until smooth. Blend in graham wafer crumbs & vanilla, mix well. Spread evenly in 23 cm square pan and chill. Melt the chocolate and margarine and pour over. Chill until it looks dull (about 30 minutes). Score and cut with sharp knife.