Mix flour, baking powder and salt; set aside. In another bowl, cream together peanut butter, butter and both sugars utnil light and fluffy. Beat in eggs and vanilla. Stir in flour mixture just until blended. Fold in chocolate chips. Spread batter in greased 8 inch glass bakin pan. Bake 25 to 30 minutes in 350 degree oven.
*Do not overbake: when done top will be browned and brownies will pull away from sides of pan while center still seems soft. Remove from oven and allow to cool at least 20 mintues before cutting into squares.
When doubled this recipe bakes in a 9 x 13" dish for 30 to 35 minutes.