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Smarties Rainbow Cake

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This easy smarties rainbow cake is a festive birthday cake with a berry filling, some smarties, and a blackberry ganache (no buttercream!).
  • Author: Delphine Fortin
  • 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).

Ingredients

Scale

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

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. 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).

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