Cream together:

1/2 c. peanut butter
1 stick butter softened

Then add:

1/2 c. white sugar
1/2 c. (light) brown sugar

Mix well then add:

1 egg
1/2 tsp. vanilla
1 1/4 c. flour
1 tsp. baking powder

Form into small balls (about the size of walnuts), place on a greased cookie sheet a few inches apart. Press balls gently with a fork. Bake in a preheated oven at 325 degrees for about 10 minutes. Watch carefully, the bottoms burn quickly (use top oven rack only). When done, gently move to a cookie rack to cool.