Melt-in-Your-Mouth Peanut Butter Cookies

1/2 cup butter (don't use margarine - butter is best)
1/2 cup solid shortening (I use butter-flavored Crisco sticks)
1/2 cup peanut butter (I use creamy - but crunchy would be good too)
1-1/2 cups powdered sugar
1 tsp. vanilla
1 beaten egg
2 cups sifted flour
1 tsp. baking soda
1/4 tsp. salt
1 tsp. cream of tartar

Cream butter, shortening and peanut butter. Add sugar and beat until mixture
is fluffy. Blend in vanilla and egg until creamy. Combine remaining
ingredients and add to creamed mixture; blend well. Roll into 1-inch balls, roll the balls
in granulated sugar, and put them on a cookie sheet; then flatten with a fork.
Bake at 350° for 12 minutes.