Inspired by a photo a friend found online, I made rainbow cupcakes for a party this summer. I was aiming to have about 30 cupcakes so I used two boxes of cake mix and made two batches of frosting. I probably could have gotten away with one batch of frosting, but I haven't made them again to be sure. Anyway, here are some notes about the process.
I promise, it's not as hard as it sounds!
Follow the directions for a regular old yellow cake mix BUT however long it says to mix it (mine said on low until combined, then medium for 2 minutes) you want to short it. If you overmix cake batter you get tunnels in the cake, and since this cake batter was going to be dyed and you have to mix in the dye I didn't want to push it. So I mixed on medium for 1min 30sec. Then I poured cake batter into 5 cereal bowls for red, orange, green, blue, and purple - the batter is yellow so you don't have to dye that one. Don't fill them all the way because you need room to stir.
I used Wilton Icing gel dyes. They can be purchased just about anywhere in the cake decorating section of a store. I used:
You can use any food coloring, but this is what I had. If you go this route you'll also need toothpicks. You dip a toothpick into the bottle and the gel sticks to it, then you stir it into the batter and discard it. I only used one dip for each of the colors you see here, and of course you never ever double dip the toothpicks! Ew!
I used white baking cups in my muffin pan, because that's what I had. I do a quick spray with Pam or similar nonstick spray on the baking cups.
I baked an entire test batch a few days beforehand to learn the hard way that you only need a little of each color. The spoons in these photos are the bigger size spoon that comes with a standard place setting, and a spoonful of each color in a cup is too much. So use less than that, really!
I'd also recommend doing all 6 colors into a couple cups first to get a feel for how much batter will wind up in the cups. Then you can switch to doing all the red, then orange, etc. assembly-line style.
I put each new color in the center of the cup, so it ends up looking like this.
Then you bake as directed - for me this was 20-25 minutes and they needed about 23. Once they cool, and YES WAIT UNTIL THEY COOL, you can frost them. I made my own buttercream using this recipe from Bakerella:
Easy Buttercream Frosting
1 cup (2 sticks) butter (room temperature)
1 teaspoon pure vanilla extract
1 1b. 10X powdered sugar
1-3 teaspoons milk, half and half or cream
* Using a mixer, cream softened butter and vanilla until smooth.
* Add sugar gradually, allowing butter and sugar to cream together before adding more.
* If you want your frosting a little creamier, add a teaspoon of milk at a time and beat on high until you get the right texture.
* Then, just use icing colors to tint the frosting the color of your choice.
I used a #21 Wilton star tip to frost them in a spiral. I cooled them on a cooling rack over a dish, so when I put on the sprinkles I could collect the escapees underneath to cut down on the mess.
I *think* that one batch of frosting would have frosted the 30 but I had some from the day before and used it too.
21 hours ago