1. Preheat the oven to 180 C / Gas 4. Grease and line a 9″ cake tin with baking parchment.
2. Beat the butter and the sugar together in a large bowl, I use an hand mixer for this as its much easier. Break the eggs into a cup and mix together.
3. Slowly add the egg mixture to the butter and sugar and whisk well, if the mixture begins to separate, sieve in a little of the flour mix
4. Add the vanilla essence and milk, and mix well. Add the baking powder to your flour and begin to sieve it into the cake mix. Stir the flour in slowly with a spatula or a wooden spoon.
5. Add gel colouring in small amounts to your mixture until the desired colour is reached. I use a toothpick for this and remember that the color will be slightly dark after baking.
6. Bake for 30-40 minutes. I test the mix by putting a knife in the very center of the cake, if it comes away clear, the cake is ready.
7. Take the cake out of the oven and allow to cool on a wire rack. When the cake is completely cooled wrap securely in clingfilm to keep fresh
8. Repeat steps 1-7 for each rainbow colour.
9. Repeat steps 1-7 for the chocolate, adding the cocoa power at step 5 instead of the gel food colouring. When we made this we didnt have a correct sized tin for our smaller cake so we used a square tin, and later cut the cake into a circle, you may have to increase the cake mixture if you do this.
10. When all the cakes have cooled, place them flat in the freezer. Don’t make the same mistake I did an stack them all as it will squash the bottom ones! Allow to freeze for at least 2 hours. You can leave them in the freezer for longer, and prepare the cake layers in advance for when needed. Take the butter out of the fridge and allow to warm to room temperature
11. Place the butter in a bowl, and mix with a electric mixer, it should pale in colour. Add the vanilla essence and icing sugar to the bowl a bit at a time, add the milk slowly if needed to create a smooth and creamy texture.
12. Remove the rainbow layers from the freezer and take off the cling film. Remove the top and bottom of each cake to create a level surface, I used a cake leveler for this, but you can use a knife. For the best finish cut all the layers to the size of the smallest cake.
13. Place a small amount of buttercream onto your cake board to secure the first cake layer, place your first layer on top in a central position, then using a pallet knife spread a layer of buttercream onto the cake. Repeat this process until all of the cake layers have been used.
14. At this point I had used all my first batch of buttercream, I made up batch number 2 and covered the top and sides of the cake, using the pallet knife to create a nice smooth finish and crisp edges, as this helps to create a smooth base for the fondant layer. This video
shows how, however the lady suggests using two layers of buttercream, I only used one, but my first layer was thicker.
15. Measure the cake to find how big your fondant icing needs to be to cover the it easily. The easiest way to do this is to take a piece of string and carefully measure from one side of the cake board, up and over the cake to the other side, then cut your string to size
16. Sprinkle your clean work surface with icing sugar, and knead your fondant icing for a few minutes until workable. Begin to roll out, turning it as you go so that it doesn’t stick. Use your string to check when your fondant is large enough. Pick the fondant icing up with your rolling pin and drape the icing over the cake. Smooth the fondant using cake smoothers, pushing out any air bubbles and creases, starting on the top then working down the sides. Use a small knife to cut away the excess icing – don’t cut too close to the cake.
17. Repeat step 12-16 for the smaller chocolate cake. You will need the a third batch of buttercream and the remaining packet of fondant icing for this. I placed the first layer of the chocolate cake onto a piece of cardboard the same size, covered in tin foil. This helps distribute the weight when you place it on top of the rainbow tier later.
18. Reserve a small section of white fondant to make a fondant number for the top, then split the leftover fondant from both cakes in to 6 even sections and add the gel colouring slowly using a toothpick until you are happy with the colours.
19. Measure around the radius of the cake with some string and cut the string to size so you know how long the zig zags need to be. To make the zigzags I rolled each colour into a long thin tube, before rolling it flat. You can use a ruler along side the icing to help keep it straight. I trimmed the fondant straight and roughly 2cm wide. Using a small square I cut away small triagle shapes to create the zigzag pattern. I forgot to take a photo, but this image explains it well.
18. Carefully stick the zigzag fondant to the rainbow cake using a small paintbrush and water.
19. I placed wooden skewers into the rainbow cake, and cut them to make them level with the fondant. This creates a firm base for the chocolate cake and prevents its sinking, then carefully place the fondant covered chocolate cake on top.
19. Roll some of the leftover icing into small balls and place around the bottom of the second tier to cover the join.
20. Roll the remaining icing out quite thickly, and use a small heart cutter to cut the hearts shapes to decorate the top tier.
21. We coloured and shaped the leftover white fondant to make a pink number 5, and secure in place with a toothpick
22. Secure the remaning fondant balls and hearts into place using a small dab of water with a clean paintbrush
23. To make bunting, dye some string using food colouring and leave to dry. When dry, tie each end of the string to the top of a skewer and position on the cake. To make the colourful flags, print out some rainbow coloured long rectangles, cut into shape, folded them over the string and glued in place
Tada! Finished zigzag rainbow cake
I didnt have a small cake tin for the 7″ cake, so i used a square tin and when the cake was part frozen I placed both layers of cake between two round bowls and used a bread knife to cut around the edges, using the bowls as a guide.
I also didnt have a smaller cake board, so I cut a piece of cardboard down to the same size as the cake, and covered it in tin foil.
You can lower the temperature of the oven, and cook for longer if you find your cake is rising too much.