Using a standing mixer, beat the egg whites, powdered sugar, vanilla, cream of tartar for 5-7 minutes until stiff peaks form
You made need to add in 1⁄2 cup more of powdered sugar depending on the consistency.
Divide the icing into 4 bowls
Mix 1 color into each bowl until you get the desired colors you like
Cut 12 circles out of the brownie bar and place onto a cookie sheet
Using whichever color you like, pipe a triangle or some odd shape onto the top of the brownie and fill it in
Repeat the same step with the remaining colors, making sure they touch
Using the black icing bag, pipe black lines over the parts where the colors meet to create Sally's “stitching”
Pipe small lines or x over the black lines to create the binding look of Sally's dress
Allow the icing to harden
Squeeze the black frosting into the last piping bag
Pipe a spider anywhere on the top of the brownies
Allow the frosting to harden for a hour
Serve and Enjoy!