Preheat oven 180 degrees C. Grease a 40 x 25 x 3cm baking pan.
Sift flour, baking powder and salt together and set aside. Using a large pan, melt the butter and stir in the brown sugar. Let this cool for about 10 minutes and then add the eggs one at a time. Be sure to beat well after adding each egg. Add the flour mixture, the nuts and the chocolate chips and blend well. Spread in the greased pan.
Bake 25 to 30 minutes in the preheated oven or until the edges begin to pull away from the sides. Cut into small squares when cool.