Preheat oven to 375 degrees.

In one bowl, combine brown sugar and white sugar. In another bowl, combine flour, salt and baking soda.

In a third bowl, use a hand mixer on medium to cream together the butter and sugars. Beat in egg, vanilla, peanut butter. Carefully sprinkle in flour mixture a little bit at a time, continuing to use the hand mixer until you have a doughy consistency.

Roll batter into small balls and place each one on a cookie sheet. Press with fork, one way and then the other, to make a criss-cross pattern.

Bake for 10 minutes. Cool on a cookie rack for about 15 minutes.