Combine flour, baking soda, and salt and set aside.
Cream together the butter, peanut butter, granulated sugar, brown sugar, and vanilla in a large bowl.
Beat in egg.
Gradually beat in flour mixture.
(If you'd like, you can add 2 cups of semi-sweet chocolate chips to the mixture, but I know*my* school could never afford such luxuries as chocolate!) Spread batter into a 13x9x2 inch pan.
Bake at 375F for 15 to 18 minutes.
(If you'd like to go the extra mile past what your school could probably afford to make for your lunches, you can take 1 cup of milk chocolate chips and put them on the surface of the peanut butter bars just after you've removed them from the oven. The bar) Let the bars it cool in the pan on a rack then cut into bars.
Note: reduced fat peanut butter for this recipe is not recommended, as it might make the bars drier than you'd like.