This easy smarties rainbow cake is a very festive birthday cake. It features a simple vanilla yogurt cake, a berry filling and a velvety blackberry ganache (no buttercream involved in the recipe). The result is impressive and delicious!
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Birthday celebrations are something very important in our family. My daughter has been obsessed with her birthday for as far as I can remember, and when the day comes she’s more than ready for it. And I’d better be too! If you can relate too, I’ve got you covered with my collection of Festive Birthday Dessert Recipes for everyone in your family!
This year, my rainbow baby (read my story here) requested a rainbow cake for a birthday. I wonder why I didn’t think about it before; it was meant to be. She loves rainbows, has a huge rainbow wall sticker in her bedroom and it just suits her personality perfectly. I’m totally bias (I mean eh, I’m the mom!), but this kid is a real sunshine, always happy and all!
Smarties rainbow cake = easy birthday cake
Honestly, what I loved about the idea of this rainbow cake as soon as my daughter suggested it is that it’s EASY to make. As much as I love the idea of birthdays, I hate all the hassle that comes with the party, making the perfect cake, and so on. Yes, like everyone else I easily find overwhelmed in the kitchen when it comes to birthday baking.
This rainbow cake is just perfect when you’re looking for a low-key birthday, that still gives you the impression that you spent hours baking it. And most importantly, the sparkles in your kids’ eyes is just priceless.
What goes into this smarties rainbow cake:
- A super simple and foolproof yogurt cake, moist and tender.
- Some blackberry jam for the filling.
- A blackberry ganache (no buttercream here, see blow for more details).
- Smarties and marshmallows for the rainbow colors and the clouds!
How to make this rainbow cake?
For the detailed instructions, head over to the recipe card further below. Here are the main steps to keep in mind when making this rainbow cake:
- Start by making the blackberry ganache. Make sure you place it in the refrigerator overnight before whipping the ganache.
- On the D-day prepare and bake the yogurt cake and allow to cool completely. Trim off the top with a serrated knife if needed, and then cut the cake in half.
- Whip the blackberry ganache until fluffy. Ensure it remains very cold when using.
- Garnish one side with blackberry jam, the other one with the blackberry ganache. Then, press the two halves against each other, the flat sides facing the outside.
- Garnish with the cold whipped blackberry ganache, and decorate with smarties and marshmallows for the clouds.
Pro tips for success
- Sort the smarties by color ahead of time, it will make your job so much easier. Also, I recommend you buy more than you actually need for the cake, just in case you end up with too much of one color and not enough of another one. Plus, everyone love smarties so the more the better!
- For a better visual effect, always use the flat bottom of the cake halves as “outside walls” for the rainbow cake. This is on this side you will add all the smarties.
- Allow the blackberry ganache to cool completely before whipping it. I recommend placing in the refrigerator overnight for best results. Then, whip with an electric hand mixer or a stand mixer equipped with the whisk, and whip until stiff peaks form.
- Tips when decorating the cake with smarties. Make sure the ganache doesn’t warm up too quickly or your smarties will fall down. If needed, place the cake back in the refrigerator during the process to cool down slightly, then go on with the remaining smarties and marshmallows. Another useful tip: apply a touch of ganache to the back of the marshmallow to ensure they stick to the wall.
How to slice this rainbow cake
Now this is a tricky question! Because I chose to decorate the cake with smarties on one side only, you can easily turn in flat and slice it into thin slices.
What if I plan a big birthday party? In this case, prepare the rainbow cake as described here for decoration and the candles. For all the other guests, simple bake another cake using the same recipe ingredients and doubling the recipe, using a rectangle baking form. You will feed as many as 25+ kids and adults around, plus the cake is super easy to slice into individual portions.
Can I prepare this rainbow cake ahead of time?
I did it and it turned out just fine. The smarties are the most sensitive part here, so I recommend you make it as close as possible to the serving day. For instance, if you’re planning a birthday party at 2PM, finish decorating the cake with smarties not later than the night before by 8 or 9PM. You might have a few smarties that will slide during the night, but I found that it was not as much as I expected and an easier fix that I anticipated too.
You may also like:
- Unicorn Cake
- Homemade Cake Pops
- The Best Flourless Chocolate Cake
- Double Chocolate Muffins
- Funfetti Cookies
- Healthy Chocolate Birthday Cake
Smarties Rainbow Cake
- Prep Time: 45 mins
- Chilling Time: 5 hours
- Cook Time: 35 mins
- Total Time: 6 hours 20 minutes
- Yield: 10 servings 1x
- Category: Desserts
This easy smarties rainbow cake is a very festive birthday cake. It features a simple vanilla yogurt cake, a berry filling and a velvety blackberry ganache (no buttercream involved in the recipe).
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We’ll send it straight to your inbox, along with weekly food inspiration!
Ingredients
For the cake and filling:
- ½ cup (4 ounces/110g)* Greek yogurt
- ¾ cup (150g) sugar
- 3 medium eggs
- 1 teaspoon vanilla extract
- ⅓ cup (90 ml) canola oil
- 1 ½ cup (180g) all-purpose flour
- 2 ¼ teaspoons baking powder
- ¼ cup (85g) blackberry jam
- Smarties (rose, red, orange, yellow, green, blue, purple…)
- 6 marshmallows
- Sprinkles, for decoration
For the blackberry ganache:
- ⅔ cup (120g) white chocolate chips
- 1 cup (240 ml) whipping cream, divided
- ⅓ cup (50g) fresh blackberries
Instructions
- Preheat the oven to 350°F (180°C) and line with parchment paper the bottom of a 9-inch (23 cm) round cake pan. Grease the bottom and sides, and set aside.
- For the blackberry ganache. Heat up the blackberries in a small saucepan over medium heat, until it turned into a thick, slightly sticky berry compote, about 3-5 minutes, stirring occasionally. Strain through a fine mesh sieve to remove the seeds.
- Add half of the cream in a glass measuring jar, and heat in the microwave until very hot and almost boiling. Slowly pour the cream over the white chocolate chips, whisking well as you go, until smooth and combined. Mix in the blackberry coulis, and add the remaining cold cream. Stir until combined. Cover both ganache with plastic wrap, making contact, and place in the refrigerator for 5 hours or ideally overnight.
- For the cake. In a large mixing bowl, whisk together the yogurt, sugar, eggs, vanilla extract and vegetable oil. Add the flour, baking powder, and stir until combined. Pour the batter into the prepared pan and bake for about 30-35 minutes or until a toothpick in the center comes out clean. Allow the cakes to cool in the pan for a few minutes, then invert onto a cooling rack to cool completely.
- If needed, trim the top domed top part of the cake, using a serrated knife. Then, slice the cake in the center in two halves.
- Whip the ganache. Using an electric hand mixer or a stand mixer equipped with the whisk attachment, beat the cold ganache until soft and fluffy.
- For assembling. Place each cake half side by side, flat side down. Garnish the top part with the blackberry jam on one half, with some of the blackberry ganache on the other half. Carefully place each half against each other in 2 half moons, with the filling in the center, and place onto a serving plate or cake stand.
- Using an offset spatula, spread the blackberry ganache in an even layer all over the cake. Add the smarties on one side to create the rainbow (I only cover one side so you can easily flatten the cake out and slice it later on). Place the marshmallow, applying a small amount of ganache behind them to help them stick to the rainbow. Add sprinkles and top, and voilà! Keep refrigerated until ready to serve.
Notes
* For more accuracy and best results, please use the metric system. You need just a little less of ½ cup yogurt, i.e. 4 ounces (or 110g).
Did you make this recipe?
Lastly, if you make this Smarties Rainbow Cake, be sure to leave a comment and give this recipe a rating, letting me know how you liked it. And of course, don’t forget to tag me on Instagram! Thank you and enjoy!
