What a special cake for two little Valentines! Milli and Spiderman are made using the frozen buttercream transfer technique. I love this technique for detailed images like these. I also love the 3D effect that it gives the cake. It may appear to be a complicated technique, but it's really not. :)
Start by finding the image you would like on your cake and print it in mirror image. I like to look for coloring pages for crisp, clear images.
Tape the printed image on a cookie sheet, and then tape wax paper on top.
Outline the image with black buttercream using a #2 tip. Here's a tip: you may already know how it can be difficult to achieve a dark black color when coloring your own buttercream. It can also have a bitter taste. What I do is keep a tube of store-bought black frosting on hand for things like this. The tube will keep for months and months, and I'm save the time and energy of coloring just a small bit of black frosting! So anyway, outline in black:
As you can see I did not outline all the little details like Mille's eyes, mouth, and flowers on her dress. I'll add them later.
Stick the cookie sheet with outlined image in the freezer for 15-30 minutes while you color the rest of your buttercream. Get piping bags ready with the different colors, using tips #2 or #3 or #4.
Remove the cookie sheet from the freezer and fill in the colors. Stay within the sections, but make sure the colored buttercream touches the black. Do not color outside the lines. (Your kindergarten teacher would be so proud!)
Now pipe with white buttercream (or whatever color your cake is being frosted in), covering the entire image. Make sure the white completely covers the black and reaches the wax paper. Use an offset spatula to smooth. (Sorry this photo is blurry, but you get the idea.)
Stick the cookie sheet into the freezer for at least 30 minutes. You want the buttercream to really firm up. Go ahead and frost your cake at this point. And do your dishes! And play with your kids! And check email! Not that I can get all that done in 30 minutes, but maybe you can. ;)
When your cake is frosted and smoothed and ready for the image, remove the cookie sheet from the freezer. At this point you have to work quickly. Make sure your hands are clean and dry. Quickly remove the tape from the wax paper and place the wax paper and image on the counter top. Gently peel away the wax paper, invert the image in your hands, and place on your cake. You have one shot at this. The buttercream with very quickly start to soften and the warmth of your hands will smear the colors if you're not careful. Again, be quick and purposeful!
The result is an adorable cake with a 3D effect!