Rainbow Birthday Layer Cake with Mascarpone Chantilly & Fresh Berries

Summer is the birthday season in my family and among my friends! Between June and August, it feels like we're celebrating someone almost every weekend. So, I thought it would be the perfect time to share this beautiful birthday cake recipe that my sister baked for my little niece's 3rd birthday.

Not only was it absolutely stunning with its colorful rainbow layers, but it was also incredibly light, fluffy and packed with fresh berries. The mascarpone Chantilly frosting is airy without being overly sweet, making this cake a real crowd-pleaser for both children and adults.

Whether you're planning a birthday party, a baby shower or simply want to bake something that will put a smile on everyone's face, this rainbow layer cake is guaranteed to impress.

Why You'll Love This Rainbow Birthday Cake

Eight soft and airy vanilla sponge layers
Light mascarpone Chantilly frosting
Filled with fresh strawberries and raspberries
Not overly sweet
Perfect for birthdays and celebrations
Easy to customize with your favorite colors and decorations

Ingredients

Vanilla Sponge Cake (4 Sponge Cakes)

Per Sponge Cake

3 large eggs
90 g granulated sugar
90 g all-purpose flour
Pinch of salt
Gel food colouring of your choice

Total Ingredients

12 large eggs
360 g granulated sugar
360 g all-purpose flour
Gel food colouring

Mascarpone Chantilly Frosting

1 kg cold mascarpone
800 ml cold heavy whipping cream (30–35% fat)
160 g icing sugar (powdered sugar)
2½ teaspoons vanilla extract

Fruit Filling

500 g fresh strawberries
200 g fresh raspberries

Feel free to substitute some of the berries with blueberries, blackberries or cherries when they're in season.

Vanilla Syrup

130 ml water
65 g sugar
1 teaspoon vanilla extract

Equipment

Four 15 cm (6-inch) cake tins (or bake them one after another)
Stand mixer or hand mixer
Offset spatula
Cake turntable (optional but very helpful)
Serrated knife or cake leveler

How to Make the Sponge Cakes

Preheat your oven to 170°C (340°F).
In a large bowl, whisk the eggs and sugar for about 8–10 minutes until the mixture becomes very pale, thick and triples in volume. This step is essential for achieving a light and airy sponge.
Sift the flour together with the salt and gently fold it into the egg mixture using a spatula. Work slowly to keep as much air in the batter as possible.
Add your preferred gel food colouring and stir just until evenly incorporated.
Pour the batter into a prepared 15 cm cake tin and bake for 22–25 minutes, or until a skewer inserted in the centre comes out clean.
Allow the sponge cake to cool completely before removing it from the tin.
Repeat the process until you have four colourful sponge cakes.

Prepare the Mascarpone Chantilly Frosting

Place your mixing bowl and whisk attachment in the refrigerator for at least 15 minutes.

Add the mascarpone, cold heavy cream, icing sugar and vanilla extract.

Whip everything together until the frosting becomes thick and smooth with firm peaks.

Be careful not to overwhip the mixture, otherwise the mascarpone may become grainy.

Make the Syrup

Bring the water, sugar and vanilla to a gentle simmer until the sugar has dissolved completely.

Allow the syrup to cool before brushing it onto the sponge layers.

Assemble the Cake

Once the sponge cakes have completely cooled, carefully slice each one in half horizontally. You should now have eight sponge layers.

Start with the first sponge layer and lightly brush it with the vanilla syrup.

Spread a generous layer of mascarpone Chantilly frosting over the sponge and top with sliced strawberries and raspberries.

Repeat this process until all eight layers are stacked.

Cover the entire cake with a thin crumb coat of frosting and refrigerate for 30 minutes.

Finish by applying the final layer of frosting and smooth the cake using an offset spatula or cake scraper.

Decorate however you like! Fresh berries, colourful sprinkles, candles or piped buttercream all look beautiful on this cake.

Storage

Store the finished cake in the refrigerator for up to 3 days.

For the best flavour and texture, let it sit at room temperature for about 20–30 minutes before serving.

Tips for Success

Bake the sponge cakes one day ahead—they're much easier to slice once chilled.
Always use cold mascarpone and cold heavy cream.
Use gel food colouring instead of liquid colouring for brighter colours without changing the batter consistency.
Don't over-soak the sponge layers; a light brushing of syrup is enough.
Chill the cake before decorating for cleaner edges.
This cake tastes even better the next day as the flavours have time to develop.