In a large bowl, mix sugar, peanut butter, shortening, milk and vanilla. Beat at medium speed with electric mixer until well blended. Add egg. Beat until just blended.
In a separate bowl, combine flour, baking soda and salt. Add to shortening mixture. Beat at low speed just until blended. Cover and refrigerate for 30 minutes.
Divide dough into thirds. Roll out evenly to 1/4 -inch thickness. Using a floured pumpkin-shaped cookie cutter, cut dough into pumpkin shapes and place 2-inches apart on ungreased cookie sheet. Repeat with remaining dough.
To make without pumpkin cutter, pinch off walnut size pieces of dough, Shape into balls. Place 3-inches apart on ungreased baking sheet. Flatten each ball with bottom of glass to approximately 3/8-inch thickness. Form into pumpkin shape. Pinch off very small piece of dough and roll to form stem - attach to the top of the cookie. With a small knife, score cookie with vertical lines to resemble a pumpkin.
Bake in batches in a preheated 375F oven for 10-12 minutes or until cookies are set and just beginning to brown. Cool on baking sheet for 2 minutes. Remove cookies to cooling rack to cool completely.
Remove about 1/4 cup of vanilla frosting and set aside. Add several drops of red and yellow food coloring ro remaining frosting. Blend thoroughly to a bright orange color. Add 1 drop green food color to the reserved 1/4 cup frosting and blend well.
Frost all but the upper stems with the orange frosting. Frost the upper stems with green frosting.
Place chocolate chips and shortening in microwave-safe bowl. Microwave on medium for 1 minute. Stir if necessary. Microwave for another 30 seconds at a time until mixture is smooth when stirred. Transfer to a resealable bag. Cut small tip off corner of bag. Pipe lines around edge and make the faces to resemble Jack O'Lanterns.
TIPS: Cookies can be baked and cooled, packaged and frozen for up to 3 weeks. Defrost thoroughly before decorating.