Preheat the oven to 350°F. Spray a 9x9 inch pan with nonstick spray.
In a medium bowl, use an electric mixer to combine the butter and peanut butter until smooth. Beat in the sugars, then beat in the eggs and vanilla, scraping the sides of the bowl as needed to get everything mixed well.
In a separate bowl, whisk together the flour, salt and baking powder. Add to the wet mixture and beat until combined. Stir in the chocolate chips.
Spread the batter evenly in the prepared pan. Bake for about 30 minutes or until the edges are beginning to come away from the sides of the pan. Let cool completely at room temperature before cutting into bars.