Easy rainbow cake is all well and good and pretty special (if you're looking for my easy rainbow cake tutorial, by the way, good luck--Blogger crashed last week and lost it. They're supposed to be manually reposting the stuff they lost, but if they don't, expect a bare bones re-do next week), but if you need a dessert that's not just regular special, but very, very, VERY special--say, for a fifth birthday party, for example--then a rainbow layer cake is where you want to go. Yes, it's more work and it takes longer, but it's not actually any harder than the easy rainbow cake.
And it looks AWESOME.
To start the rainbow layer cake, mix up a double-batch of white cake. I don't care if you make your batter from scratch or use a boxed mix, but I do care that you mix up WHITE cake, not yellow. You'll get the best results with your dye by using white cake.
Preheat your oven and grease as many 8" round cake pans as you own. I own two, but if you borrow even just a couple more than that, you'll make this process a LOT easier. You can also make this layer cake with pans of different shapes and sizes, but then you'll have to experiment with baking time.
Scoop one cup of cake batter into a separate bowl, and dye it one color. It's most efficient to bake your layers in reverse rainbow order--you'll be building your cake from the bottom up, so if you bake violet and indigo first, then you can get started while red and orange are still cooling. I let all my layers cool overnight, though, so I dye and bake them in whatever order I feel like, so please yourself.
Scrape the one cup of dyed batter into its own cake pan, and use the back of a spoon to smooth it out over the bottom of the pan:
Bake these super-thin cake layers for approximately 15 minutes (you probably know if your oven cooks on the fast or the slow side, but if you don't, check on it after about 12 minutes), and let them cool completely.
When you're ready to decorate, melt white chocolate (harder to use) or white candy coating (also in the baking aisle and easier to use, although the ingredients are all total crap for you). You can use a double-boiler or the microwave, but my method of choice, which I also use for building gingerbread houses, is a fondue pot:
Put a dab of melted white chocolate down on the cake plate, then rest your bottom cake layer on top of that. Spread melted chocolate all over the top of that layer, then stack your next cake layer on top, and so on and so on:
It looks beautiful now, but when you cut into it, that's when everyone gets really excited, because I hate to brag on myself, but it is kind of the coolest thing ever:
Birthday Girl agrees: