Completely line 13x9-inch (3.5L) baking pan with foil. Arrange a single layer of crackers over bottom of pan. Arrange a second layer of crackers to cover spaces between crackers in first layer. (It will be necessary to break some crackers in half so that the entire bottom of pan is covered.) In medium saucepan combine sugar and butter. Cook and stir over medium heat until mixture comes to a boil. Remove from heat; pour evenly over crackers in pan. Bake in 200ºC (200C) oven 5 minutes. Remove from oven; sprinkle with chocolate chips. When chips are soft, spread over top. Sprinkle with nuts. Chill until chocolate is set. Break into pieces to serve. Store in refrigerator.