Preheat oven to 350°F. Grease and flour a 9x13 pan. Set aside. In medium bowl, whisk together flour, baking powder and salt. Set aside.
In large mixing bowl, combine melted butter and brown sugar. Cool slightly. Beat in eggs, one at a time and add vanilla extract. Add dry mixture and mix well. Stir in chocolate chips and nuts.
Pour into prepared pan and spread evenly. Bake for 35+-40 minutes or until tester comes out clean. If edges are browning more quickly than the middle, cover with aluminum foil. When cool, cut into 24 squares.
Use room temperature ingredients. You want your eggs to be the same temperature as everything else so it easily combines.
Sometimes the edges brown more quickly than the middle so cover it with foil if that's the case.
Let the blondies cool slightly before cutting them so you can get clean cuts but also some gooiness.
If you want a thinner blondie that isn't as chewy, bake in a 10x15 pan. Just keep in mind the baking time will only be about 25-30 minutes.