First preheat oven to 350°F. Cream butter, brown sugar and peanut butter until smooth. Then add the egg. Next add the vanilla, baking soda, and flour. Mix until combined. Roll them into balls and place on a cookie sheet or spray with nonstick cooking spray. Flatten them out to about 3/4 of an inch, and bake for 7-8 minutes. This recipe should make 20 cookies.