Spray bottom of a round pan, I used a disposable foil pizza pan.
Mix all brownie ingredtions till well blended. pour into pan. Bake for 35-40 minutes. Cool for 1 hour at rooom temperature.
Frost cake with chocolate frosting.
Choose a center point for the web. It may not necessarily be the center of the cake.
Starting from this center point, draw lines to the edge of the cake all the way to the sides. Join these lines with scalloped lines and complete concentric circles all over the surface of the cake as shown in the picture.
Decorate the cake with a plastic spider. You can even add plastic bugs to the web.