Today we’ll be making an organic mini square rainbow cake, colored with all natural, non-toxic food colors. We’ll top it off with fluffy vanilla icing.
- Naturally colored – because why give your kids fake color chemicals?
- Mini square – because small and square is cute – plus usually lower calorie than having a huge cake around.
- Rainbow – because who doesn’t adore rainbow cake?
Ample time! This is not a project to do on a whim because the homemade dyes take a bit of effort. On the plus side, the frosting whips together super fast.
- Make your food dyes: 1-2 hours
- Mix, bake, assemble and decorate your cake: 2 to 3 hours
Before you get started, you may want to read: pros and cons of rainbow baked goods made with natural food coloring and dyes.
PREP STEP – choose your cake size
I wanted a square rainbow cake, but don’t have square baking pans, so I used my 9 by 5 inch bread pans.
This recipe makes enough cake batter for 8 to 9 layers made in bread pans. Depending on how you divide your cake layers up, this recipe makes enough layers for either two mini square 8 to 9 layer cakes or three mini square 5 to 6 layer cakes. You can also simply make a long loaf cake, by baking the cake in your bread pans then stacking the layers. That would be cool too.
If you want to make a typical round cake, you can totally do that. To make one normal sized cake, use 8 or 9 inch pans, dividing the batter equally into as many layers as you like (six layers would work well).
You can also make and color your batter, then layer it in reusable baking cups for adorable rainbow cupcakes. Or even try making a swirl cake!
I’m using an adapted recipe for one of the best white cakes I’ve tried, along with HANDS DOWN the best ever super fluffy vanilla frosting I’ve tried. But really, you can use any white cake recipe you like. You can also choose your own frosting, although I’ll point out that this frosting is REALLY good – not too thick or sweet, but just sweet enough, plus light and airy.
Organic flour & sugar vs. conventional
Organic flours and sugars are unbleached and darker than conventional flours and sugars, which are processed differently and usually bleached crystal white. The less white your batter is, the less it’ll take on natural food dye, which begs the question – should you go conventional for a really white cake?
To see if it really makes a difference, I’ve tried making rainbow cake with both conventional and organic flour and sugar. Color-wise, the cakes aren’t THAT different. You still get a white cake batter if you go organic, it’s just not quite as pure white as conventional. The difference once the batter is colored, is negligible, as you can see in the image above.
The cake made with conventional cake flour ended up with layers that were a little more pastel colored, but also keep in mind that I took the conventional picture outside, so it’s naturally brighter AND I made the organic cake with organic whole wheat pastry flour vs. regular organic white flour (pastry flour is a bit darker).
Taste-wise, I thought the organic cake was way better, but of course, I love organics so I’m an impartial judge. Although everyone else in the house liked the organic cake better too – and the rest of the folks here don’t adore organics like I do.
Overall, I think organic is way more important than super white baked goods, so I suggest you find a decent organic white flour and stick with that, but if you want to go conventional so you can use real cake flour, at least buy from a reputable company like Bob’s Red Mill – they make an Unbleached White Pastry Flour.
Cake & Frosting Ingredients
- 5 large organic egg whites at room temperature
- 3/4 cup whole organic milk at room temperature
- 2 and 1/4 teaspoons pure Fair Trade, certified organic vanilla extract
- 2 and 3/4 cups organic white flour, sifted (or other flour of your choice)
- 1 and 3/4 cups organic granulated sugar
- 1 tablespoon + 1 teaspoon baking powder
- 3/4 teaspoon salt
- 12 tablespoons unsalted organic butter, softened and cut into cubes
- Natural food dyes – see below
Fluffy vanilla bean frosting…
- 3 sticks + 2 tablespoons of organic, unsalted butter
- 2 teaspoons pure organic Fair Trade vanilla extract
- 3 cups organic powdered sugar
- 3 tablespoons organic milk
- Pinch of salt
- 1 organic vanilla bean – scraped – optional
STEP 1 – make your natural food dyes
You’ll need about 2-3 TBS of homemade food dye for each cake layer. If making mini cakes you can make up to about 7 to 8 different colors per mini cake. If making a big cake, you can choose 6 to 8 colors, depending on how thick you want your layer.
To make your natural, homemade food coloring, read my tutorial: Make Natural Food Dyes for Organic Baked Goods Without a Juicer. You can make your homemade dyes up to a few days before baking your cake, if you like, or do it all on the same day.
STEP 2 – get your pans ready
Lightly grease the bottom and sides of your pans with a dab of organic olive oil (or whatever oil you keep around). Place cut pieces of unbleached parchment in your pans. Grease the parchment a little as well, again with organic oil. Dust the pans with flour. Set pans aside.
If you only have a few pans on hand vs. enough for all the cake layers at once, be sure to re-oil and re-parchment, oil and flour your pans for each new cake layer you bake.
STEP 3 – mixing the cake batter
Preheat oven to 350°F – I don’t normally preheat (to save energy) when making breads and other baked goods, but I do preheat when making most cakes.
- In a small bowl, combine and stir the egg whites, 1/4 cup of milk, and the vanilla.
- Using a larger bowl, combine all your dry ingredients together. I use an inexpensive handheld mixer for this, but you can mix by hand too.
- Add all of the butter and the other 1/2 cup of milk. Mix on low speed (or by hand) until just moistened. Increase your mixing speed and mix for about 2 minutes.
- Scrape the sides of the bowl to make sure everything is mixed well.
- Add your egg mixture in THREE separate batches, beating on medium speed for 20 seconds after each addition.
STEP 4 – coloring the cake batter
Gather up all your food dyes you made during step 1. Grab some bowls and a spatula.
Divide your batter into equal parts. For this recipe, I suggest scooping out 3/4 cup of cake batter per layer (for a mini square cake). This will give you about 8 or 9 long layers of cake.
The amount of color you add to your batter depends on what size cake you’re making and how much batter you’re using per layer. In general, the following rules apply…
- Use about 1/4 cup (4 tablespoons) of food dye to color 2 cups of batter.
- Use about 2-3 tablespoons of food dye to color 1 cup of batter.
- Use about 1-2 tablespoon of food dye to color 1/2 cup of batter.
To color your cake batter, choose a food dye, and add one tablespoon of color to start. If the color seems lackluster, which it likely will be with just one TBS, add another tablespoon.
Below is typically what I use to color one 3/4 scoop of batter, but results vary, so play around (see a full cake color gallery here).
- Bright green – 2 tablespoons spinach juice
- Lighter green – 2 teaspoons green tea powder
- Dark pink – 1 and 1/2 tablespoons of beet puree
- Bright yellow – 1 full dropper of yellow Chocolate Craft liquid food coloring
- Peach / light yellow – 1 and 1/2 tablespoons of carrot puree
- Purple – 2 tablespoons blackberry juice
- Light pink – 1 tablespoon strawberry puree
- Violet – 1 tablespoon raspberry juice
- Dark blue – 2 and 1/2 full droppers of Chocolate Craft liquid food coloring
- Dark blue/purple – 2 tablespoons of blueberry juice
- Orange – 4 full dropper red + 1 full dropper yellow Chocolate Craft liquid food coloring
- Light blue – 1 full dropper of blue Chocolate Craft liquid food coloring
What to do with leftover food dye? Freeze leftover produce purees and juices in ice cube trays. Put the cubes in a container and save them for the next time you make homemade ice popsor smoothies.
STEP 5 – baking & cooling your cake
- After you color all your batter, pour into your prepared pans and bake for 14 to 20 minutes (depending on how hot your oven runs).
- Watch the cake closely, because as soon as you can insert a toothpick and it comes out clean, it needs to come out of the oven. If it’s not done at 14 minutes, check it at 1 minute intervals.
- Let the pans cool on racks for 10 minutes.
- Loosen the sides of the cake with a small silicone spatula (so you don’t scratch your pans) and invert onto lightly greased wire racks.
- Gently turn cakes right side up.
- Cool completely.
STEP 6 – make your fluffy white frosting
This frosting is EXCELLENT if you like very light, creamy and not too sweet frosting. Plus, it’s easy.
- Use an electric mixer, hand mixer or big ol’ spoon to whip the butter for about 5 minutes until it becomes very pale and creamy.
- Add all your remaining ingredients and mix on low speed for 1 minute, then on medium speed for 6 minutes. The end result is super light, creamy and fluffy frosting.
This is best used right away, but it actually maintains its airy quality well over a few days (your cake likely won’t last that long though). If you like, you can use some of your natural food dyes to color your frosting, or leave it white.
STEP 7 – decorating your cake
Guess who you shouldn’t trust to teach you how to decorate a cake? Yup, me. I bake well, but my cake decorating skills are seriously lacking. Frosting and me, well, we don’t get along so great… In any case, below are the best tips I’ve got for you.
To get started, first cut each cake layer in half – if making mini square cakes.
OPTIONAL STEP – I usually wrap each cooled cake layer in parchment, then freeze all the layers for a few hours. This makes your cake way easier to frost, but it’s an optional step.
Once your cake is well frozen, unwrap enough cake slices for one mini cake. If you want to, level them off carefully with a sharp knife. I’m a little lazy, and it’s not like my kids care if my cake if perfectly flat, so I usually skip leveling the cake. Arrange the layers in a stack. to see which color order the layers look good in.
To frost, place your first layer on a platter. Plop some frosting on, spread the frosting out to the edges of the cake, place the next slice on, and go from there.
Once all your layers have frosting in between them, trim the sides of the cake (if need be) to make the sides more even. This helps you get the frosting on better. Now you should have a decently squared off cake to decorate…
Here’s where I start having problems. Basically, what I do is frost the top and sides with a thin layer of frosting to seal in crumbs. Then I place a lot more frosting on the top and sides, then smooth it out as best as I can. Again, I’m not a cake decorating genius! If you want some excellent cake decorating tips, read Whisk Kid’s How to Frost a Cake.
I try to follow Whisk Kid’s directions, but it’s still hard for me. Also, I don’t have a bench pastry scraper, because frankly I’m not motivated to get one (I rarely make heavily decorated cakes). Whisk Kid recommends one though if you want to decorate perfectly frosted cakes. Since I don’t have a bench scraper, I fold a piece of heavy paper into fourths, and use the edge of that (it works okay).
Whisk Kid explains how to do corners – which I’m STILL not good at, so if I want to hide shoddy corners, I’ll use piped frosting to make a little design of frosting on the corners (as shown above). You can do this too if you like. It works really well if you’re not great with cake corners.
STEP 8 – serving your cake
This part is easy! Cut carefully with a sharp knife, eat and enjoy. This makes a great birthday surprise cake. When I sliced into the cake the kids at my house all went, “Ohhhhhh!”
One mini cake sliced thinly (it’s rich) gives you about 8 to 10 slices.
STEP 9 – storing your cake
This cake is best the first day, but still great for a couple of days after. To store leftovers, place in a cake holder or wrap tightly in foil and store at room temperature. This cake can be refrigerated for up to 5 days. Layers can be frozen for up to 2 months.
Hope you enjoy it. Let me know in the comments if you try it out.