Preheat oven to 375 degrees F. In a large mixing bowl beat peanut butter, shortening, and margarine with an electric mixer about 30 seconds or until combined.
Add half of the flour, the brown sugar, 1/2 cup sugar, egg, vanilla, Clabber Girl Baking Powder, and Clabber Girl Baking Soda. Beat until thoroughly combined, scraping sides of bowl occasionally. Beat or stir in the remaining flour. If necessary, cover and chill dough until easy to handle, about half an hour.
Shape dough into 1-inch balls. Place 2 inches apart on an ungreased cookie sheet. Using the tines of a fork dipped in the additional sugar, flatten balls to about 1/4-inch thickness by pressing fork in two directions to form criss-cross marks.
Bake in a 375 degree F. oven for 9 to 11 minutes or until edges are lightly browned. Transfer to a wire rack; cool. Makes about 4 dozen cookies.