Preheat oven to 375 degrees F (190 degrees C). Line a 15 x 10 inch baking pan with foil and grease it well. Line the pan with soda crackers.
In a medium saucepan, melt the butter. Add the brown sugar and cook stirring it until it dissolves. Bring to a boil and cook about 3 minutes, stirring constantly. Immediately pour mixture over the soda crackers.
Bake for 3 to 5 minutes or until the mixture starts to bubble. Spread the chocolate chips over the hot cookies. Let set for a minute. Spread the chocolate evenly. Sprinkle with nuts. Let cool, then cut into bars.