Cream together the butter, sugar, peanut butter, egg and vanilla extract. Sift together the flours, baking soda and salt. Add the flour mixture to the creamed mixture and mix until smooth.
Preheat oven to 375°F. Set aside an ungreased cookie sheet.
Shape teaspoonfuls of dough into balls by rolling between the palms of your hands to the size of a walnut. Place dough rounds 2" apart on cookie sheet. Flatten lightly with the tines of a fork that have been dipped into flour. Press the tines into the dough making a crisscross design.
Place oven rack in middle position of oven with cookie sheet and bake for 10-12 minutes, until set, but not hard. Allow to cool for 3-4 minutes and remove from cookie sheet to wire rack. After cookies have cooled they can be stored in an airtight container for up to 4-5 days.