• Preheat oven to 350°F.

Working with one box of cake mix at a time, bake the cakes:

• Prepare 2** 8" or 9" cake pans by lightly greasing the sides and bottom and then dusting lightly with flour. For added insurance, you can place a parchment round in the bottom of the pan and grease that before you flour the pan.
• Combine cake mix with water, egg whites and vegetable oil. (Follow the recommended mixing time on the box.) Fold in 2 oz of jimmies/sprinkles. Divide the batter between two cake pans and bake per the box instructions. Cool cakes for 15 minutes, then un-mold to a cooling rack. Wash and dry the baking pans. Repeat steps to bake the 2nd box.
  

Assemble the cake:

• If necessary, level the cooled cakes. Using a biscuit cutter or ring mold, cut a hole in the center of THREE layers only, leaving enough of the outer sponge to have a sturdy cake.
  
• Stack the three holey cake layers, applying icing between each layer.
  
• Fill the hole with your mix of candy, sprinkles and spiders — all the way to the top. Add the last layer of cake to the top and finish applying the icing. 
• Chill the frosted cake for 15 to 20 minutes (or longer for store-bought icing) to firm up the icing.
• Microwave marshmallows for 30 seconds and give them a stir. They should be melty and stringy when you pull on it. If they don’t stretch yet, give them another 15 seconds in the microwave.
  
• Remove the cake from the fridge. Using two forks or your fingers, pull and stretch the marshmallow over the cake in all different directions. Add a couple spiders for the full effect!