This rainbow cake seriously took me less than 3 hours total, including baking, making icing, decorating, etc.
Round cake, baked & cooled (I used an 8"x3" round cake.)
Icing, colored blue (I used my cream cheese icing)
Any other color icing & tip #3
Bake the Cake
my complete tutorial on doctoring your cake mixes.)
one of my favorites. This way, when I cut it in half, I wouldn't have to worry about having layers to hold together when covering the sides with sprinkles.
If you don't have an 8"x3" pan, you can absolutely use an 8" or 9" round pan that is thinner. You can then just glue the two halves together with icing when you cut it in half. And you could then use the rest of the cake batter to make cupcakes or something.
Make the Icing
Cream Cheese Icing, and colored it light blue with a few drops of food coloring. I figured blue sky behind the rainbow made the most sense, right?
my post about finger-licking if you're worried about the 5-year-olds having dirty hands.)
I was nervous to coat the side/top of the cake with the sprinkles because I've never done this before. It wasn't as bad as I feared.
The nice thing is that you really don't have to worry too much about crumbs because they'll be covered with sprinkles anyway. But, you do want to try to make it relatively smooth. You can see if there are weird spots of thicker icing when you cover it.
Don't put too much icing on the side. I learned that when you roll it in the sprinkles, it smooshes the icing and spreads out a little. You don't want it to get too spread out, or it makes covering the sides harder.
Once you get the sides covered, you are ready to roll (literally).
I did have a few times when the sprinkles got a little too thin on the plate, so the icing stuck to the plate (eek!). Be careful that you have a thick layer of sprinkles, and that you can shake the plate to get them back into a thick layer before you move it.
Admittedly, the second cake I rolled went much better than the first. I think if/when I do this again, I'll be able to do it even better.
For the most part, who cares if the sprinkles mix in, because it's going to be covered with the M&Ms anyway.
Decorator's Buttercream that develops a crust, be careful that you don't wait too long to add the M&Ms, or it may be harder to get them to stick.
You have to get a little creative in a few spots when you get towards the bottom because they don't all line up perfectly, but once you add your marshmallow "clouds," you're good to go!
*Note: The M&Ms lose their "crack" when you refrigerate the cake in an airtight container. So if you like that hard candy coating, don't make this too far in advance.
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