Preheat the oven to 350 degrees. Butter your 9x13 inch cake pan and place in the fridge until needed.
In a bowl, sift all of your dry ingredients: flour, carob powder, cocoa powder, baking powder, salt; set aside.
In a stand mixer or by hand, whisk all wet ingredients: milk, oil, vanilla, aquafaba; until well combined.
Next, add the dry ingredients until batter is smooth and lustrous; gently fold in the chocolate.
Pour all of the batter into the cake pan; place in the oven and bake for 30-40 minutes until the tooth inserted into the center comes out clean.
Once done, set to let cool overnight (in the fridge is okay as well).
With the cake completely cooled, remove from the cake pan (carefully) and divide the cake into two equal halves. To make sure the cakes are flat, use a serrated knife to carefully trim down the bump of the cake.
Frost the top of your first layer with the buttercream and top with the other half of the cake. Frost the top and sides with buttercream with a crumb coating; place in the freezer for 1 hour.
While the cake is in firming, roll out your white fondant for the sides of the cake and the brown fondant for the spine and cover of the book, making sure the fondant is ¼ inch thick.
Remove the cake from the fridge and attach the fondant to the cake (tip: use a brush to with a bit of water the brush the sides and top of the cake before carefully/gently adding the fondant). Using a fondant smoother, gently smooth down the sides and top making sure there are no air bubbles present.
With the spare brown fondant, roll a small amount into thin strands to create the pentagram and a small amount of fondant into a thin long strand for the circle of the pentagram. Secure them with a little bit of water and a small brush.
Optional: The Glass Demon Eye is made with Isomalt and edible eye wafer paper.
Conjure, cut and serve to the mortals and immortals of your choice.