1. Make cookies: In a small bowl, whisk flour, baking powder and salt.
2. In a medium bowl, using an electric mixer on medium-high speed, beat butter and shortening until well combined. Add sugar; beat until light, about 2 minutes. Beat in egg, then vanilla. Stop mixer and scrape down sides and bottom of bowl. With mixer on low speed, add flour mixture to butter mixture until just combined. Scrape down bowl and mix again until dough forms. Place dough in a large ziplock bag and seal bag. Roll out dough in bag to 1/4-inch thickness. Refrigerate for at least 3 hours.
3. Preheat oven to 375ºF. Gently open ziplock bag and cut away 2 sides, then peel bag away from top of dough (as though opening a book). Flip dough out onto a lightly floured surface and peel away remaining plastic. Cut with a 4-inch pumpkin-shaped cookie cutter and place 4 cookies each on 2 ungreased baking sheets. Bake until edges are firm and turning golden brown, 12 to 14 minutes, switching sheets halfway through. Let cool on baking sheets on wire racks for 5 minutes, then remove cookies to racks to cool completely.
4. Make icing: In a bowl, combine butter, milk and vanilla. Whisk in confectioners' sugar until smooth (icing will be thin and pourable). Transfer about 1/4 cup icing to a small bowl; dye with green food coloring. Dye remaining icing with orange food coloring. Spoon green icing onto pumpkin stems. Spoon orange icing over rest of cookies. Add candy corn as eyes and licorice for mouths. Let stand at room temperature for at least 6 hours to allow icing to harden.