Preheat the oven to 350 degrees. Lightly grease and flour a 9 by 13-inch baking pan and set aside. Sift flour with salt, baking soda, baking powder and set aside.
Melt butter in a large sauce pan over low heat. Add the brown sugar, remove it from the heat and stir until completely blended; let cool to room temperature. Add eggs one at a time stirring well after each addition. Stir in the vanilla.
Transfer the mixture to a large mixing bowl. With a rubber spatula, fold the sifted flour into the batter with a few smooth swift strokes and stir just until batter is blended and smooth. Do not over mix or the blondies will be heavy. Stir in the chips and nuts and pour into a prepared pan. With a spatula, spread the batter to make sure it is even in thickness. Bake for 35 to 40 minutes until the top springs back when you press it lightly with your fingertips or when a toothpick, when inserted in the center of the dough comes out clean.
Remove the blondies from the oven and let them set until completely cool. Cut into rectangles and wrap individually in plastic or foil to keep them very fresh.