In a large bowl, sift together flour, Rumford Baking Powder and salt.
In a medium bowl cream together shortening and sugar until light and fluffy.
Add eggs and vanilla; mix well. Add sifted dry ingredients; mix well. Chill at least 30 minutes up to 2 hours.
Preheat oven to 375° F. Grease two cookie sheets or line with parchment paper and set aside. Roll out on floured surface. Cut with 2-inch cookie cutter; sprinkle with granulated sugar. Make an indent in the center of the cookie with your thumb-this will help to keep the chocolate balls in place.
Bake on greased cookie sheets at 375° F, for 10 minutes or until the edges are golden brown.
To prepare the frosting: In a medium bowl whisk together the powdered sugar and cocoa.
In a separate bowl, beat the butter until smooth and add the sugar/cocoa mixture, 1/2 cup at a time, beating until incorporated. Add 2 tablespoons of the heavy cream, vanilla extract and beat well on medium speed. If the mixture is too stiff, add more milk until the mixture is creamy.
When the cookies have completely cooled, pipe some of the frosting in the center indent on each cookie. Place a chocolate candy ball on top. Pipe additional frosting on the candy balls to place 2 candy eyes on each spider body. Use the frosting to draw out the spider legs.