I started this Jack Skellington cake by making one 1/4 sheet vanilla and 1/4 chocolate and iced them together with buttercream icing to make a flat surface. I put the cake briefly in the freezer to harden the icing so that it is easier to smooth (especially the sides) but not too long or it will crack the icing when thawing(like a crackle finish in painting).
I had to color the background because Jack is white to make him stand out. So I used blue food coloring spray to color the cake instead of blue icing to give it an uneven effect. I then used a simple shell border in white. I then put the cake aside and pulled a piece of wax paper out.
Using the same tip as the shell border I started in the middle making a big swirl with the white icing and then froze it till hard. I took a spatula and scraped icing away until surface was smooth. I took black icing and decorated his face. Peeled away wax paper and place it on cake. I finished with the black frame and writing.