1Preheat the oven to 350. Lightly grease a 13x9 baking dish with butter or oil. Sift the flour, baking powder, baking soda and salt together into a small bowl and set aside.
2Using an electric mixer on medium speed, cream the butter, sugar, and vanilla in a medium size mixing bowl until light and fluffy, about 1 1/2 minutes. Scrape the bowl with a rubber spatula.
3Add the eggs one at a time and beat on medium speed after each addition until partially blended, 5 seconds. Scrape the bowl, then beat until the batter is blended, 20 seconds more.
4With the mixer on low. Add the dry ingredients and beat until almost blended, about 15 seconds. Scrape the bowl. Add the chips and mix on low until blended in. Stir batter several times with spatula. Spread evenly in the prepared pan.
5Bake the bars on the center oven rack until top has risen and set, and is golden in color, 26 to 28 minutes (The top won't spring back when touched; a depression remains) Allow the bars to cool for 1 hour on a rack before cutting. *These can also be made in an 11x7 baking pan.