Stack 4 to 5 layers of butter cake, spreading the buttercream in between layers. Cover the whole cake with the icing. Refrigerate for an hour. Carve into a cauldron shape.
Color the fondant accordingly, black, orange and green.
Roll a black fondant enough to cover the cauldron. Cover the cake.
Mold black fondant into a shape of a cauldron handle. Attach into the sides of the cake.
Roll a green fondant and cut it into a size that would fit the top of the cauldron.
Use the rice krispies to mold into small balls, this would be the contents of the cauldron. Cover it with some of the green fondant.
Attach these small green balls on the top of the cauldron.
With the remaining of the fondant, use your creativity to add up other characters to the cake, a cat, a wizards hat or a wizard’s legs.