I am so happy with how this butterfly birthday cake turned out. I owe my success to another "Coolest Cakes" butterfly photo (the orange and black monarch). As I explain below, I use the baker's technique of tracing the image with black gel and pressing it onto the cake to make an outline.
Here's how I made this cake:
I searched online for butterfly clip art. I found a butterfly outline that I liked, and I enlarge it in Word to the size I wanted the cake. I then printed it out (it took 3 papers). I taped the papers together to make one large butterfly. I trimmed the taped papers to give about 1/2 inch of paper around the outline of the butterfly.
I baked two 9x13 cakes. When the cakes cooled, I trimmed off the edges of the cakes (all four sides) so that the cakes would sit flush to each other. I placed them side-by-side on a piece of cardboard. I used a large bread knife to trim the tops of the cakes down so that the top surface was even and flat.
I then placed the trimmed print-out of my butterfly on top of the cakes. I trimmed the cakes to the shape of the butterfly, leaving about one inch extra cake around the printout. I then let my kids eat the cake scraps (so they would leave my nice cake alone :) while I frosted the butterfly outline in white.
I then took my print-out of my butterfly and a tube of decorative black gel icing (the little white tube from the grocery store). I used the gel to trace the entire butterfly print-out. Then I took my gel traced print-out to the cake. I turned the print-out upside down (gel-side down), and I set it onto the frosted cake. I gently pressed the paper onto the cake, making sure I pressed every part of the paper down very gently. I then carefully peeled off the paper to reveal a black butterfly pattern.
I used a small round tip to fill in the outline. My daughter (turning 5) was absolutely thrilled with the cake. Her little girlfriends gathered around the cake at the beginning of the party and admired it for quite a while before I had to shoo them away and get the party started. All of the girls thought it was delightful.
I used Wilton frosting colors. By tracing the outline with the gel, the possibilities were awesome! I knew I would never be able to free-hand it, so the idea from the other baker was really what made this cake possible.