Preheat oven to 400 degrees.  Place crackers in a single layer on a foil-lined 10X15" cookie sheet.  Heat butter and sugar in a saucepan on medium heat until butter is melted and mixture is well blended.  Bring to a boil and boil for 3 minutes without stirring.  Spread over crackers.  Bake 7 minutes.  Remove from oven and immediately sprinkle with chopped chocolate:  let stand 5 minutes.  Spread melted chocolate evenly over ingredients in pan:  sprinkle with nuts.  Cool.  Cut or break into pieces.  Makes about 8 servings.