Pastel Rainbow Cake Recipe – Easter Cake Ideas – Rhubarb Crumble Cake, Streusel Cake

25. March 2022
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Prep time: 3 hours

Serves: 12

This pastel rainbow cake recipe is one of the best Easter cake ideas! Above all, this Easter cake recipe tastes incredibly delicious because underneath the rainbow and the chocolate Easter eggs you’ll find a a moist crumble cake with vanilla buttercream on top and a fruity rhubarb filling. A super delicious Easter cake design made easy with these step-by-step instructions.

Rhubarb Crumble Cake

Since it is one of my Easter cake recipes, I also wanted to keep the taste very spring-like, so I decided to make an easy rhubarb crumble cake for this rainbow cake recipe. A delicious and moist batter with the classic crumble on top. Then comes vanilla buttercream and a refreshing, homemade rhubarb filling, making a really delicious rhubarb cake.

For the rhubarb crumble cake recipe, first mix butter until fluffy (room temperature), add sugar and salt and continue to mix, then mix in one egg (room temperature) at a time for about 30 seconds. Lastly, mix flour with baking powder and add milk and vanilla. Mix everything together to obtain a nice batter.

For this cake batter, it is particularly important that all the ingredients are at room temperature, otherwise the batter will become lumpy due to cold ingredients. Line three 16cm / 6 inches diameter baking pans with baking paper and grease and flour the sides of the baking pans and evenly spread the batter in them.

There are many Easter cake ideas and Easter cake designs out there, but this one is truly unique because it contains a rhubarb cake recipe. For the crumbles or streusel, mix flour, butter and sugar with clean hands until you obtain crumbles, spread them evenly over the three cakes and bake at 160°C / 320°F for about 30-40 minutes. 

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How to make Easter Cake Decorations

This pastel rainbow cake without is made with the most delicious German or Ermine buttercream, my absolute favorite buttercream because it consists 2/3 of pudding, thus not that greasy! A layer of this buttercream is spread on the cake layers and then topped of with a fresh rhubarb filling, which resembles an easy rhubarb custard cake.

For this easy rhubarb and custard cake recipe, wash the rhubarb well and cut into thin slices. If threads come loose while cutting, simply peel them off and throw away. Place the rhubarb in a saucepan and heat it up together with sugar and cornstarch, stirring constantly until everything becomes a homogeneous filling. As soon as it starts boiling, the filling starts to become thick, transfer to a bowl and cover with cling film.

Rainbow Cake Recipe

How to make Easter Cake decorations? For the rainbow look we’re using a German vanilla buttercream! For the German buttercream, place almost the entire milk to a boil in a saucepan, mix the remaining milk with the sugar and cornstarch and when it starts boiling add the mixture while constantly stirring with a whisk and continue stirring until it boils again. As soon as it begins to thicken, transfer to a bowl, add vanilla flavor, mix and then press cling film onto the pudding surface so that no pudding skin can develop.

When butter and pudding are at room temperature, mix the butter until fluffy and then add the pudding spoon by spoon. The tastiest and best frosting for this rainbow cake rainbow icing!

Decorations for Rainbow Cake Design

Decorations for Rainbow Cake design are not that tricky if you follow these steps. In order to make Easter baking for this mini egg cake easy we use the same frosting for the filling and outside. This has two advantages, first, the buttercream keeps the crumbles crispy and fresh because the buttercream hardens when the cake is chilled and, second, we don’t have to make a second frosting for the filling since this easy rhubarb cake already has two different ones.

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After the rainbow celebration cake is finished and crumb coated, spread the remaining buttercream in six different bowls and color five of them in a pastel colors, I just used a little bit of food coloring for the following colors: pink, yellow, green, blue and purple.

Fill all the colored frostings into piping bags and mark equal space on the rainbow high cake for each color. With the piping bag pipe the colors onto the cake and smooth out the sides with a cake smoother. Finally, warm the cake smoother in hot water, dry it and then work it around the cake at a 45° angle to have it perfectly smooth. Pipe buttercream on the top of this Easter egg cake and decorate the rainbow cake with chocolate sprinkles and chocolate mini Easter eggs. Now it’s time to enjoy this easy Easter cake with mini eggs.

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Print Recipe

Pastel Rainbow Cake Recipe

  • Preparation time: 3 hours
  • Servings: 12

Ingredients

Streusel / Crumble Cake

  • 150g (1/2 cup + 3 tbsp) butter, (room temperature)
  • 90g (1/2 cup) sugar
  • 1 pinch salt
  • 4 eggs, (room temperature)
  • 260g (2 cups) flour
  • 3 tsp baking powder
  • 120ml (1/2 cup) milk
  • 1 tbsp vanilla
  • 120g (1 cup) flour
  • 70g (1/3 cup) butter, (room temperature)
  • 45g (1/4 cup) sugar

German / Ermine Vanilla Buttercream

  • 1 liter (4 cups) milk
  • 100g (3/4 cup) cornstarch
  • 100g (1/2 cup) sugar
  • 1 tbsp vanilla
  • 500g (2 + 1/4 cup) butter, (room temperature)

Rhubarb Filling

  • 150g (1 + 1/2 cup) rhubarb
  • 50g (1/4 cup) sugar
  • 20g (1/4 cup) cornstarch

Decorations

  • food colorings, pink, yellow, green, blue, violet
  • chocolate sprinkles
  • 12 small chocolate mini eggs

Method

Streusel / Crumble Cake

  • Mix 150g / 1/2 cup + 3 tbsp butter until fluffy (room temperature), add 90g / 1/2 cup sugar and salt and continue to mix, then mix in one egg (room temperature) at a time for about 30 seconds. Lastly, mix 260g / 2 cups flour with baking powder and add milk and vanilla. Mix everything together to obtain a nice batter. Lay out three 16cm / 6 inches diameter baking pans with baking paper and grease and flour the sides of the baking pans and evenly spread the batter in them. For the crumbles or streusel, mix 120g / 1 cup flour, 70 / 1/3 cup butter and 45g / 1/4 cup sugar with clean hands until you obtain crumbles, spread them evenly over the three cakes and bake at 160°C / 320°F for about 30-40 minutes.

German / Ermine Vanilla Buttercream

  • For the German buttercream, place almost the entire milk to a boil in a saucepan, mix the remaining milk with the sugar and cornstarch and when it starts boiling add the mixture while constantly stirring with a whisk and continue stirring until it boils again. As soon as it begins to thicken, transfer to a bowl, add vanilla flavor, mix and then press cling film onto the pudding surface so that no pudding skin can develop. When butter and pudding are at room temperature, mix the butter until fluffy and then add the pudding spoon by spoon.

Rhubarb Filling

  • Wash the rhubarb well and cut into thin slices. If threads come loose while cutting, simply peel them off and throw away. Place the rhubarb in a saucepan and heat it up together with sugar and cornstarch, stirring constantly until everything becomes a homogeneous filling. As soon as it starts boiling, the filling starts to become thick, transfer to a bowl and cover with cling film.

Assembly

  • Put buttercream into a piping bag and pipe a ring around the edge of the first crumble cake, then spread a layer of buttercream on it and spread half of the rhubarb filling on top. Repeat this step and finally place the last crumble cake on top. Cover everything in a thin layer of buttercream using a palette for a crumb coat, this helps to keep the crumbs in the first layer of buttercream so they won’t get into the outer layer of buttercream.

Decorations

  • Spread the remaining buttercream in six different bowls, it should be approx. 100g for each bowl, and color five of them in a pastel colors, I just used a little bit of food coloring for the following colors: pink, yellow, green, blue and purple. Fill all the colored frostings into piping bags and mark equal space on the rainbow high cake for each color. With the piping bag pipe the colors onto the cake and smooth out the sides with a cake smoother. Finally, warm the cake smoother in hot water, dry it and then work it around the cake at a 45° angle to have it perfectly smooth. Pipe buttercream on the top of this Easter egg cake and decorate the rainbow cake with chocolate sprinkles and chocolate mini Easter eggs.

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