Serves 8 to 12.
For the cake layers:
- 60g butter
- 80g sugar
- 1/8 tsp salt
- 1 egg
- 1/2 tsp vanilla extract
- 1/4 cup milk
- 100g all-purpose flour
- 1/2 tsp baking powder
- Gel food colouring in red, orange, yellow, green, blue, and purple
This recipe makes 2 layers, so bake this recipe three times in total.
For the buttercream icing:
- 300g butter/shortening or combination of
- 1 tsp salt
- 1 tsp clear imitation vanilla flavouring (or regular vanilla extract if you don’t have it)
- 600g icing sugar, sifted
- About 1/2 cup milk
- White food colouring (opt.)
Step 1: Preheat your oven to 175°C (350°F). Grease and line two 6-inch round cake tins.
Step 2: Cream the butter and sugar together until light and fluffy. In a bowl, beat the egg, vanilla extract and milk together. In another bowl, sift together the flour and baking powder. Add half the liquid and dry ingredients to the butter-sugar mixture and beat in well. Add in the remaining liquid and dry ingredients and beat in.
Step 3: Divide the batter evenly between two bowls. Dye each bowl of batter a different colour with about 1/2 tsp of food colouring. Pour each batch into a prepared cake tin and bake the tins for 30 minutes. Cool and set aside and get on to making the recipe two more times, dying each layer a different colour until you have 6 cake layers in red, orange, yellow, green, blue and purple.
Step 4: When you have six cake layers of different colours, get on to making the icing as they cool. In a mixer (or large bowl if doing by hand), beat the butter/shortening, salt and vanilla for about 3 minutes to incorporate, then add the sifted icing sugar in small batches, beating well between batches. Thin it to a spreadable consistency with the milk. If you’d like a pure-white icing, substitute some of the milk with white food colouring.
Step 5: To assemble the cake, torte each layer so that they’re even. (I wouldn’t skip this step — it’s a tall cake, so uneven layers will become even more pronounced.) Start with the purple layer, add about a quarter cup of icing (remember — tall cake, so go easy on the icing), spread it out evenly and then add on the blue layer. Repeat for the remaining layers.
Step 6: Apply a crumb coat with the icing and chill it in the refrigerator for about 30 minutes or until the icing has crusted. Smooth the remaining icing evenly around the cake. (Here’s how to get smooth sides.) Decorate the cake as you desire.