Preheat the oven to 375 degrees. Butter cookie sheets and set aside. With an electric mixer beat the butter until soft. Add the sugars and beat until creamy. Add the egg, peanut butter, salt, baking soda and vanilla.
With a rubber spatula fold the flour into the egg mixture but do not overmix. Roll the dough into small balls and place them on prepared cookie sheet. With a fork press the balls into flat cookies and bake for 15 to 17 minutes or until crisp and golden.
For added touch melt some bittersweet chocolate in a double boiler remove and cool down a bit. When still pliable dip one edge of cookies into chocolate.