In a large sauce pan melt the butter. Add the sugar, corn syrup, and water. Cook over medium heat, stirring now and then; to hard-crack stage (300 on your candy thermometer) watch carefully after temperature reaches 280.
Quickly stir in coarsely chopped nuts; spread in well-greased pan. Cool thoroughly.
Turn out on waxed paper; spread top with half the melted chocolate; sprinkle with half the finely chopped nuts.
Cover with waxed paper; invert; spread again with remaining chocolate.
Sprinkle top with remaining nuts. If necessary, chill to firm chocolate. Break into pieces.