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tutorial: tiniest rainbow cupcakes birthday cake

🌈 What's better than a surprise inside rainbow cake? A birthday cake with the tiniest mini cupcakes on it! Because I'm a little much sometimes, I top the cake with a mini buttercream cloud cake. Because adults need cute things too! Anyways, stay to cake decorate a birthday cake with mini cupcakes and a rainbow cloud cake topper. Thanks so much for joining me here!

See my video for a demonstration:

Most asked questions:

  • I have a peanut allergy (or my friend does), do I have to Reese’s peanut buttercups? Nope! There are so many “peanut butter cup” style molds. You can use white chocolate or candy melts to fill them and create this same exact project.

  • I don’t feel like rainbow.. do you think solid “cupcakes” will look cool? Well yeah!! Go for it and do you xoxo.

  • If you have any questions – dm me on Instagram #cakeideas #minicupcakes #cakedecorating


· Stand mixer

· Mixing bowl

· Angled spatula

· 5” or 6” round cake pans

· Cake board

· Cake scraper

· Cloud cake mold

· Piping bags

· Your favorite star piping tip (I like the Wilton #32 and #21)


How to make Swiss Meringue Buttercream

Step 1 – make 2 batches of this Swiss meringue buttercream.

Step 2 – coloring the buttercream. Split your buttercream in half – this will be for the cake filling, crumb and frost. I chose to color this yellow. With the rest of the buttercream, I split this, color this rainbow minus the color I’ve used for the base which is yellow. Set each color in a different piping bag and set aside. I made pink, red, orange, green, blue, and purple. You’ll end up with ¾ cup (or so) for each color.

  • Tip: You can stage one piping bag with a coupler and your favorite tip; and use it for all of the piping of miniature cupcakes. Just switch the colors in between.

How to make a surprise inside rainbow tie dye cake (can be done 2 days before and frozen):

Step 3 – make vanilla cake batter.

Step 4 – mixing the batter into colors. Add a little batter into 6-8 bowls. Add a different color into each bowl. Mix mix mix! Then distribute the rest of the batter and incorporate thoroughly.

  • Tip: I mix the batter in stages to get the most even color distribution.

  • Tip: remember it’s easier to add than remove color!

RoxStarBakes Rainbow mini cupcake cake
RoxStarBakes Rainbow mini cupcake cake

Step 5 – distributing the batter for baking. Distribute the rainbow batter across your four 5-inch cake pans that are lined with parchment paper (this is clearly demonstrated in my video). Use a knife or angled spatula to pull the batter to the sides (score the batter). Then bang the batter to release any extra-large air bubbles and also fill in the edges. Bake for according to the recipe or use a toothpick to see if the baking is complete - there should be about 5 crumbs.

  • Tip: It’s best not to grease the sides so the cake batter can climb the sides of the pan as it bakes. I love tall and fluffy cakes!

  • Tip: Loosen the edges with a thin knife or angled spatula and place on a cooling rack to cool completely.

  • Tip: Make sure the cake is cooled before assembling.

RoxStarBakes Rainbow mini cupcake cake

Step 6 – leveling the cake. Once cooled, level the cake. I use a bread knife but there is no one way to do this. Save these scraps to make the cake topper.

How to make decorative miniature rainbow cupcakes:

Step 7 – coloring the Reese’s peanut buttercups. Color the tiny white peanut butter cups in edible luster dust of any color (I chose white) to give them a distinctive sparkle and shine. I even add edible glitter. See how the ones I’ve dusted shine below when compared to a regular ‘cup’.

RoxStarBakes Rainbow mini cupcake cake

Step 8. Pipe a little swirl on top of the peanut butter cup to make a tiny cupcake. A Wilton #21 or #32 tips work perfectly.

Step 9 – sprinkling. Decorate with non-pareile sprinkles. So cute!!!

  • Tip: sprinkle from higher up to prevent a ‘too dense’ sprinkling.

  • Tip: Refrigerate for 10 minutes to avoid ‘smushing’ while cutting.

Step 10 – cutting the mini cupcakes. Heat you knife. Cut! Place on parchment lined cutting board and place in fridge until ready to use.

How to make a mini cloud cake topper:

Step 11 – using the cake scraps. Cut the cake scraps into rectangle shaped pieces. Frost the insides of a cloud-shaped mold with some buttercream, all the way up the sides. Cover the sides enough so none of the sides are exposed. Tap air bubbles after the frosting is applied. Place cake slices inside of the mold. I think two slices fits great. Frost the ‘bottom’ of the cloud and then refrigerate for 30 minutes. When they’re cold enough, they will pop out of the mold easily.

Step 12 – adding the face. Decorate with a cute kawaii face made from fondant, and place on the top of the cake.

  • Tip: If you don’t know Jack, you should really meet him! Jack, my super cute smiley face cloud cake topper is making a reappearance with some edible matt luster dust to his cheeks to make him appear even happier! You can find more on his story in this video here.

How to assemble the rainbow cake:

Step 12 – filling and crumb coating. To assemble the cake, place 1 cake layer on a cake stand and adhere with buttercream or meringue. I use an ice cream scooper to evenly portion the filling and then use an angled spatula to evenly level. Top with a second cake layer and press firmly so the cake adheres. Continue building until the all layers are placed. Use the yellow frosting to crumb coat the cake by spreading on a thin layer of frosting and then scraping the excess away. It’s a thin layer of frosting to lock in the moisture and capture the crumbs. Then place in the refrigerator for 15-30 minutes.

  • Tip: You can use a level to ensure the cake is leveled.

  • Tip: Make sure the cake is completely cold.

  • Tip: Make sure to press gently between each cake layer to ensure the cake is secure.

Step 13 – frosting the cake. Continue adding frosting to the cake. I find it’s quickest to use a piping bag for the distribution. Tighten the frosting with an angled spatula. Then use a cake scraper to smooth and remove any excess.

  • Tip: The cake is fresh for three days and can be kept in the fridge. Allow to get to room temperature before serving for best flavor.

  • Tip: Once you’ve sliced the cake, if you place plastic wrap where the slice is removed, it keeps the cake fresher and prevents drying.

Decorating the cake:

Step 14 – adding the cupcakes. Make sure your cake is VERY cold. Market where you’d like the columns to be on the cake. I use sprinkles but recommend lightly marking the top of the cake with a knife. With a toothpick add a bit of melted white chocolate to the back of each mini cupcake. Press the top of the peanut butter cup against the cake and hold for a few seconds. Alternate the angle of each cupcake half for a great visual effect. Refrigerate along the way if the cupcakes get too warm.

  • Tip: Candy melts work great too.

Step 15 – place the cloud topper. DONE!

Rainbow mini cupcake birthday cake success!!!


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