Line a 15x10x1-inch baking pan with foil. Place crackers in a single layer to completely cover bottom of baking pan (cut crackers to fit, if necessary). Set the pan aside.
In a medium saucepan, combine butter and sugar. Heat and stir over medium heat until mixture boils; boil gently for 3 minutes. Pour butter mixture evenly over crackers. Bake in 375 degree F oven for 5 minutes.
Remove from oven and sprinkle immediately with chocolate pieces. Let stand for a few minutes to melt; spread chocolate evenly over all.
Sprinkle with nuts, pressing lightly. Chill. Cut into squares or diamonds to serve. Makes about 48 cookies.