1. Preheat the oven to 350°F (176°C). Line the bottom of three 8-inch (20cm) cake pans with parchment paper and grease the sides.
2. Beat butter and sugar until light in color and fluffy, about 3-4 minutes.
3. Add eggs one at a time, beating just until blended.
4. Add vanilla, water and cocoa powder to another bowl and whisk until smooth.
5. Add chocolate mixture to batter and mix until combined. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Combine flour, baking soda and salt in a separate bowl.
7. Alternate adding the flour mixture and milk to the batter. Begin by adding half of the dry mix, then mix well. Add the milk and mix well, scraping down the sides as needed. Add the remaining flour mixture and mix until smooth.
8. Divide batter between the cake pans. Bake for 26-30 minutes, or until a toothpick inserted comes out with a few crumbs.
9. Remove cakes from the oven and allow to cool for 3-4 minutes, then remove from pans to a cooling rack to finish cooling.
10. While the cakes cool, make the frosting. Beat the butter and shortening together until smooth.
11. Slowly add about 1/2 of the powdered sugar, mixing until smooth between each addition of powdered sugar.
12. Add the vanilla extract and 3 tablespoons of water to the frosting and mix until smooth.
13. Slowly add the remaining powdered sugar, mixing until smooth between each addition of powdered sugar.
14. Add additional water to the frosting, as needed to get a smooth consistency.

TO PUT THE CAKE TOGETHER:

15. Use a large serrated knife to remove the domes from the tops of the cake layers so that they are flat.
16. Place the first layer of cake on your serving plate or on a cardboard cake circle.
17. Spread 1 cup (240g) of frosting into an even layer.
18. Add the second layer of cake, then another cup (240g) of frosting.
19. Top the cake with the third layer of cake.
20. Frost the outside of the cake with the remaining frosting. For help getting a smooth finish, refer to my tutorial on how to frost a smooth cake with buttercream.
21. Pipe a swirl border of frosting around the top edge of the cake. Set the cake aside.

TO DECORATE THE CAKE:

22. To make the chocolate ganache, add the chocolate chips to a metal or glass bowl. Microwave the heavy whipping cream until boiling, then pour over the chocolate chips. Cover the bowl with clear wrap for about 5 minutes, then whisk chocolate until smooth.
23. Use a spoon or piping bag with tip to drizzle chocolate down the sides of the cake, between each frosting swirl.
24. To make the white chocolate ganache, add the white chocolate chips to a metal or glass bowl. Microwave the heavy whipping cream until boiling, then pour over the white chocolate chips. Cover the bowl with clear wrap for about 3 minutes, then whisk chocolate until smooth. If needed, microwave the mixture for another 5-10 seconds, then continue whisking until smooth.
25. Reheat the chocolate ganache slightly, if needed, then spread remaining chocolate ganache evenly onto the top of the cake, inside the border.
26. Pipe a swirl onto the top of the chocolate ganache, starting from the center of the cake and spiraling out towards the border of the cake.
27. Use a toothpick to create the web effect. Place the toothpick in the center and drag it out towards the border to create a line. I drew 8 lines total.

TO MAKE THE SPIDERS:

28. Melt the orange melting chocolate and place into a piping bag with a small round tip (I used a Wilton 4). You could also use a ziplock bag with a corner cut off. Pipe the legs in the shape of an “L”. You’ll need 6 legs per spider, for about 3 or 4 spiders. Repeat with the dark cocoa melting chocolate. (See photo of example of spiders)
29. Once the legs are made and cooled, set out 4 or 5 circles of melting chocolate for the bodies. Working with one leg at a time, pipe a small dot of melted chocolate onto the side of the body and place a leg is position. Hold it in place for about 30 seconds, or until you can take your hand away and it stays in place. Add 3 legs to each side of the body.
30. To make the eyes, microwave the chocolate on 10 second intervals, stirring between each until melted, and pipe the eyes onto the bodies.
31. Place the spiders on top of and around the cake.
32. Refrigerate the cake until ready to serve. The cake is best served at room temperature.