My first rainbow cake. It was bound to happen eventually. But surprisingly, this is the first time after four and a half years of baking for this blog. Friends would look at me funny and say, "Are you sure you've never made a rainbow cake before?!". I've done rainbow sprinkle ombre cakes and rainbow-shaped cakes but for some reason I never went for the full rainbow cake experience.
I remember the first time I laid eyes on a rainbow cake. It was on Kaitlin's amazing Whisk Kid blog and it blew my mind. Back then I had never seen anything like it and I was completely smitten. I remember thinking to myself that I would probably never have the talent and precision to make anything that perfect. And since then so many others have made equally impressive versions of the rainbow layer cake. It had been done. I remember wishing I could have it as my wedding cake but I wasn't able to get it. Sad face!
But then a couple of weeks ago I had the challenge of coming up with a crazy birthday cake for my friend Regex Man. It's been getting pretty hard to beat my previous efforts for his birthday, most of them have turned out to be some of the most popular cakes on this site including the mint chocolate chip cake. I finally decided that this would be the perfect time to try my first rainbow cake. Sure it was nothing original but it was SO MUCH FUN. I've learnt so much about assembling layer cakes over the years and surprisingly this cake came together without much stress or mishaps. The important thing to remember; be patient! I baked three layers of this cake one night, three layers the next night and then iced it the morning after. Trying to do everything on the same day would have been exhausting.
I did have a bit of a disaster when it came to decorating the outside of the cake. Originally I wanted to create this big complicated cake bunting thing by threading jelly beans together but I am so not a crafty person and it turned into a huge ugly mess of wasted jelly beans and string. So I went to plan B and just topped the cake with rainbow jelly beans. You can't really go wrong with that, especially when there is so much going on inside of the cake. I made sure that the colours really popped in the cake layers, I wasn't looking for a half-arsed pale/pastel rainbow, I wanted it to be really intense (It's so intense!) in colour. I used gel colouring because I know you get a really bold colour without having to use huge amounts. If you have a problem with using food colouring then this obviously isn't the cake for you. There's always natural food colouring options but I wanted the full-blown crazy rainbow effect and you can't get that with natural food colouring.
I get a lot of questions about how I get my layers neat and even and icing smooth. I learnt from some great tutorials from other great baking blogs (here, here and here) and it's taken a bit of practice to get better at it. As I said, patience is the key. You need to give your cakes time to chill, they are so much easier to cut neatly if you chill them first. I always turn my cake layers upside down (at the very least the top layer) as it tends to help keep them level when you stack them. An offset spatula will make your life so much easier when you are smoothing your icing. Crumb coating. All these little things make a big difference. I still can't get the edges perfectly straight and even but I've always been a messy baker.
Doesn't it make you happy just looking at it? I was expecting it to be nothing special to eat but I was actually really pleased with the taste. I used my trusty yellow cake recipe, the same as I've used for most of my vanilla layer cakes. The icing is just regular salted butter icing but with lots of lemon juice to help cut through all that sugar. I took extra care this time to make sure I didn't overbake my cakes at all, I took them out as soon as the skewer came out clean. The result was 6 layers of soft vanilla cake that wasn't the least bit tough or dry, even after all the mixing and chilling in the fridge. It was a little tricky to serve the cake as full-sized six-layer slices, so we ended up cutting it up into two layer slices. Obviously I went for a purple-blue piece.
Rainbow Layer Cake with Jelly Bellys
(makes a six-layer 18-20cm cake, serves approx 40)
For the six layers of cake: (divide by 6 if you want to bake each layer individually)
530g (about 4 cups) plain (all-purpose) flour
6 tsp baking powder
3/4 tsp salt
340ml (about 1 1/3 cups) milk
4 tsp pure vanilla extract (if using essence reduce to 3 tsp)
600g (about 2 1/2 cups) sugar (I use caster/superfine but white/granulated is fine too)
340g (3 sticks) butter, softened
6 eggs, at room temperature
Food colouring (I used Wilton gel icing colouring, about 1/4-1/2 tsp per layer)
Preheat oven to 180°C (350°F) and grease whatever 18cm (or if you prefer, 20cm) round cake tins you have (I have 3 so I split the amounts listed above in half and did three cakes at a time. If you only have 1-2 tins you can prepare all the batter ahead of time and bake them one after another but the last cakes might not rise as much. You can also mix and bake one layer at a time, but this is very time consuming.). Line the base of tins with baking paper and grease paper. Combine flour, baking powder and salt in a medium bowl and set aside. Mix milk and vanilla together in a measuring jug or bowl.
Using an electric mixer on low speed, beat sugar and butter in a large bowl until blended. Increase speed to high and beat until pale and creamy, at least 5 minutes. Reduce speed to medium low, add eggs 1 at a time, beating well after each addition. Alternately add flour mix and milk mixture, beginning and ending with flour mixture (I did it by adding 1/4 of of the dry mixture followed by 1/3 of the wet mixture at a time). Beat until smooth, occasionaly scraping bowl with a spatula. Divide mixture evenly into 6 medium bowls (I did this by weighing the batter on kitchen scales to ensure consistency). Gradually mix in colouring until you are satisfied with the colour (gel colours will be more vibrant after baking). Try to avoid over mixing the batter, but it is quite forgiving. Pour batter into prepared tins and bake each layer for about 20-22 minutes or until a skewer into the centre comes out clean and the outside is golden, take care not to overbake or cakes will be tough. Cool in tin for 5 mins and then turn out onto wire racks to cool completely. Wrap in clingfilm and chill overnight.
For the lemon icing:
(Note: I am only guessing at the right amounts here as I had to make extra icing to cover this cake. You may need to adjust the amounts/ratio to get the right icing consistency and volume)
800g (about 6 1/2 cups) icing (powdered) sugar, sifted (or blitzed in the food processor)
400g (about 3.5 sticks) butter (I use salted, add about 1 tsp of salt if you use unsalted)
1-4 tbsp lemon juice (or milk mixed with vanilla extract if you want vanilla icing), adjusted to taste/consistency
Prepare the icing; remove butter from fridge 30 mins before starting and chop into small cubes. In a large mixing bowl, beat butter on high with an electric mixer until smooth and fluffy. Reduce speed to medium-low and gradually add icing sugar until combined, then increase speed to high and beat until very pale and fluffy. Gradually add lemon juice to taste, you may need to add more icing sugar if your mixture is too runny, or more lemon juice or milk if you mixture is too stiff. The icing should be smooth and easily spreadable, but stiff enough to hold its shape.
To assemble cake; remove cake layers from the fridge and use a long shape knife (preferably serrated) to carefully trim the tops of the cake to ensure they are level. Flip your cake layers upside down before assembling. Place the purple layer on your cake plate/stand, spread a thin layer of icing over the top with an offset spatula (I used an ice cream scoop to ensure equal amounts between each layer, about 1 generous scoop for each layer). Repeat with the blue, green, yellow, orange and red layers. Crumb coat the cake and chill for about 15 minutes, then cover the cake with more icing and smooth out surface with an offset spatula. For a smoother finish, run your offset spatula under hot water and dry with a paper towel regularly.
Optional: To decorate; cover the top with rainbow jelly beans, or m&ms or skittles. Or you can cover the entire cake in rainbow sprinkles like this.