- 165g unsalted butter, softened, plus extra for greasing
- 400g caster sugar
- 5 large egg whites
- 11/2 teaspoons vanilla extract
- 115g soured cream
- 375g plain flour
- 1 tablespoon baking powder
- 1 teaspoon bicarbonate of soda
- 1/2 teaspoon fine salt
- 240ml whole milk
- Food colouring pastes (purple, blue, green, yellow, orange and red)
- For The Cream Cheese Icing
- 250g unsalted butter, softened
- 350g icing sugar, sifted
- 250g full-fat cream cheese
- 1 teaspoon vanilla extract
- You Will Need
- 1 disposable piping bag
- Preheat the oven to 180 °C/gas 4. Grease and line 3 x 20cm cake tins and 3 x 18cm cake tins with baking parchment.
- Using an electric hand whisk, beat the butter and caster sugar together in a large bowl until light and fluffy. Add the egg whites, one at a time, beating well after each addition. Lightly beat in the vanilla extract and soured cream. Sift the flour, baking powder, bicarbonate of soda and salt into a bowl, then add to the egg white mixture in three batches, alternating with the milk. Fold through evenly with a large spoon.
- Divide the mixture between six smaller bowls. Take a rounded tablespoon out of three of the bowls and add one to each of the other bowls. Add a little purple, blue and green food colouring paste to the fuller bowls and yellow, orange and red colouring paste to the smaller bowls, mixing until combined.
- Spoon the purple, blue and green mixtures into the 20cm cake tins, spreading evenly. Bake for 10–12 minutes, or until a skewer inserted into the centre comes out clean. Leave to cool for 5 minutes, then turn out onto a wire rack and leave to cool.
- Spoon the yellow, orange and red mixtures into the prepared 18cm cake tins, spreading evenly, then bake and cool as above.
- Once the cake layers are cold, using a serrated knife, carefully trim the crusts off the edges of the cakes. Use the base of a slightly smaller cake tin or an upturned plate to cut around.
- For the icing, beat the butter and icing sugar together in a bowl until light and fluffy. Gradually beat in the cream cheese, a spoonful at a time, then beat in the vanilla extract until smooth. Spoon one-third of the icing into the piping bag, then snip a 1 1/2 cm hole off the tip. Pipe a circle of icing around the inner edge of the purple sponge, then fill the centre in with a few tablespoons of icing and spread out evenly. Top with the blue sponge and then repeat the icing steps with the remaining icing, leaving the top of the cake un-iced.
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