675 g (1.49 lb / 5½ sticks) unsalted butter, plus extra for greasing
675 g (1.49 lb / 3 cups) superfine sugar
1 tbsp vanilla extract
12 medium or 10 large (about 500 g) eggs
675 g (1.49 lb / 5 cups) self-raising flour
1 tbsp baking powder
½ tsp each of red, orange, yellow, green, blue, purple food colourings
500 g (1.1 lb / 4 sticks) unsalted butter
1 kg (2.2 lb / 8 cups) powdered sugar
3 tbsp milk
1 tbsp vanilla extract
Sprinkles (eg. hundreds and thousands) (optional)
Preheat the oven to 190 °C (374 °F). Grease and line six 20 cm (7.9 in) round cake tins.
Beat the butter, sugar and vanilla in a large mixing bowl, until soft and fluffy.
Beat in the eggs, two at a time.
Combine the flour and baking powder. Fold this dry mixture into the batter.
Divide the mixture into 6 separate bowls.
Add the red food colouring, one drop at a time, to the mixture in one bowl and stir in until the mixture reached the desired colour.
Repeat step 6, using orange, yellow, green, blue and purple food colourings.
Spread the red mixture in one of cake tin. Repeat with other colours.
Bake for 25 minutes, in batches of two cakes, until a skewer inserted comes out clean.
25 minutes
Transfer the cakes to a wire rack and leave to cool. Unmold cakes.
For the icing, beat the butter in a mixing bowl until soft.
Add half of the icing sugar, 1 cup at a time, and beat in.
Beat in the milk and vanilla extract.
Add the rest of icing sugar, 1 cup at a time, and beat in.
Spread one-eighth of the icing onto the purple cake. Top with blue cake layer, and press gently.
Repeat the frosting and cake layering in rainbow order, finishing with the red layer.
Spread the rest of icing all over the cake.
If you like, sprinkle the cake with sprinkles.
Enjoy!
- •Gel food coloring is better than dilute liquid coloring. Using more concentrated coloring will result in more vibrant colors.
- •Mixing the food coloring into the cake batter after the flour is added can make the cake tough due to the additional stirring needed. Be careful to only mix as much as necessary.