1. Preheat oven to 350 degrees F. Spray a 9 by 13 inch pan with nonstick spray.
2. In medium bowl, combine flour, baking powder, and salt. Set aside.
3. In large bowl, use an electric mixer on medium speed to cream together butter, peanut butter, and sugar for 2 to 3 minutes, until well blended. Beat in eggs and vanilla just until combined.
4. With mixer on low, alternately add flour mixture and buttermilk, in three additions each, starting with flour. Mix just until blended, scraping down sides of bowl after each addition.
5. Stir in peanuts, peanut butter chips, and chocolate chips.
6. Spread batter into prepared pan and bake at 350 degrees F for 35 minutes, or until it turns golden and tester comes out clean, and surface is firm to the touch. Transfer pan to a rack and cool for 15 minutes before cutting into 24 squares. Store in an airtight container at room temperature for up to three days, or wrap and freeze for up to one month.
Source: Hannaford fresh Magazine, May - June 2007