Ingredients:
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260g all purpose flour
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100g cake flour
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2 sticks butter, 1 cup
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⅓ cup coconut oil
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2 cups sugar
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1 teaspoon salt
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2 teaspoons pure vanilla
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1 teaspoon imitation vanilla
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2 teaspoons baking powder
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4 egg whites, at room temperature
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1 cup buttermilk, room temperature
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Assorted food coloring
Method:
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Preheat oven to 325.
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Butter and flour a large bundt pan.
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Begin by sifting together the AP flour and cake flour into a bowl. Set aside.
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Cream butter, coconut oil and sugar together for a full 5 minutes or even more, until very light and fluffy. Add salt, vanillas, and baking powder and whip for a few more minutes.
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With the mixer on, add egg whites, one at a time, allowing each to be fully incorporated before adding another. This beats air into the batter so add slowly.
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Add half of your flour mixture, and mix until just combined.
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With mixer on low, add buttermilk in a slow drizzle. Add rest of flour and beat just to combine
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In 5 separate bowls, add about 4-5 tablespoons of batter. Using gel food coloring add red, yellow, green, blue and purple to each bowl and stir to combine the colors. Use about 2/3rds of the remaining batter to fill your bundt pan. Leave the last third for the top, to cover the rainbow.
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Begin by filling a piping bag with red and make a circle within the bundt on top of the white batter. Make the border of the circle pretty thick by circling several times - you are going to be making 4 more circles with thinner borders within it. Use the back of a teaspoon to smooth out the red batter and even it out in preparation for the yellow.
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Do the same with the yellow, making it slightly less thick (leaving a slight space on either side so the red is still visible. Continue with the green and so on, until you have a thin circle of purple.
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Use a spoon to gently add the rest of the white batter on top. Smooth top over with an offset spatula.
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Bake for about 45-50, checking for doneness after 40 minutes.
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Allow cake to cool for about 15 minutes in pan, then invert onto a cooling rack.
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Once cake is totally cool drizzle with ganache or glaze.
Notes:
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You’ll need to use a large bundt pan to make this, any shape will do but consider how the rainbow will look once the cake is baked. A bundt is usually turned upside down so we’ll build the rainbow beginning with red - making the red fatter and gradually decreasing the width of the border of the circle as you move through the colors, ending with purple. I tried this in a brilliance bundt, a tube pan and a ring mold - the last gave me the best results because of the curvature on the bottom which gave me a nice upside down U shape that made the perfect rainbow. (Bonus: my ring mold also made it look like a giant donut!)
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The link I have above to the cake pan takes you to a 9” ring mold, this is the one I have and use but it is always a tight fit for my batter. I believe the 10” would be a safer bet.
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My recipe is a mash-up of various white and lemon cakes I use regularly. I use a bit of cake flour here because of all the stirring that goes into coloring the rainbow batter. I chose a ‘white’ batter because I wanted the canvas for the rainbow to be pure so the colors would stand out. To do this, you need to leave out the yolks from your recipe. So, based on a tip from BraveTart who does this in her white mountain cake recipe, we’ll add coconut oil to replace the moisture lost in removing the yellows.
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I used 5 colors to make my rainbow as I found that the orange wasn’t necessary and too many blues/purples just created a deeper coloring on the bottom. Build the rainbow you want but make sure you use five colors!
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I did a simple white vanilla glaze on one of the cakes (1 cup powdered sugar, 1 teaspoon imitation vanilla and 1 tablespoon milk) and a white chocolate ganache (100g white chocolate, 60g heavy cream) on another, but really the options are limitless! Color it to whatever tickles your fancy. My daughter suggested a dark chocolate ganache and I was so tempted - if you try this I need to see it!
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Special baker’s tools needed here are: piping bags, an offset spatula, and food coloring.
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Update June 2019: a how-to video I posted on my Instagram highlights.
Rainbow Pound Cake by ButterMilk