Rainbow CakePosted: July 1, 2017
Regular listeners might remember, back in October (2016), my oven died a week before my daughter’s birthday, which ended up resulting in a six-month wait for an entirely new kitchen. I promised to make her a birthday cake when the new kitchen was installed, and the request was put in for a rainbow cake. A few glitches here and there, meant that I only got around to it a couple of weeks ago.
This is not that cake. That cake I didn’t photograph. That cake was just for her, and consumed at all times of the day and night, including breakfast, until she waved the white flag in defeat. The idea for this cake came out of that cake.
It also gives me an opportunity to have a bit of a rant over a pet peeve of mine, namely food colouring. Yes, in a post about rainbow cake, I’m going to complain about food colouring.
Regular viewers might remember previous rants including making-stuff-look-like-stuff-it-isn’t, featuring the infamous Come Dine With Me chocolate shoe incident. A few weeks ago, I revealed my dislike of over-the-top recipes. Rainbow cakes are now part of the Things-Which-Induce-Much-Gnashing-And-Grinding-Of-Teeth.
The usual way to make a rainbow cake involves seven layers of luridly-coloured sponge cake, interspersed with dollops of unnaturally-white buttercream. Then the whole is smothered with more highly-coloured sweets or fondant or buttercream, etc, etc. Sometimes the brightly-coloured sponge is mixed together in blobs, but in general the format is pretty standard, and it all involves So. Much. Food. Colouring.
But none of this is a patch on the über villain when it comes to coloured cakes, the Red Velvet Cake.
What originally started out as a reddish hue from a reaction between the cocoa and the vinegar/buttermilk has, in the 21st century, turned into a virulent-red chocolate cake dyed with food colouring. Bottles of the stuff. Modern, concentrated gel colours mean that not as much, by volume, is required, but still. It’s a chocolate cake, people. And it’s red. Bright red. Think about that. Enough colouring to turn a chocolate cake red.
And with both red velvet and rainbow cakes, the cake itself doesn’t strike me as being particularly nice, quite apart from the American penchant for making them up using *Matilda Response* box mixes.
I wanted to see if it was possible to make a rainbow cake using the bare minimum of food colouring, that actually tasted nice, and so here we are.
The answer lies in the classic Joconde Imprime, which you may well remember from the Great British Bake Off Season 2 and my Chocolate & Orange Mousse Cake and the miniature Strawberry & Rhubarb cheesecakes from my Finale showstopper: A coloured, pound-cake paste is used to draw a design onto baking parchment, then frozen. A light, almond sponge mixture is then poured over and smoothed out, before baking in a hot oven for 5-7 minutes. When the cake is turned out, the pattern is visible on the underside of the sheets, which can then be used to make entremet-style desserts. ‘Course, back then, an orange squiggle or a red stripe was considered pretty cutting edge. Nowadays it looks tame.
Usually, the Joconde paste is piped into the desired pattern, but once cooked it can make for a rather clunky contrast with the sponge (pound cake mix vs light, airy Joconde). One solution would be to use a teeny, tiny piping tip but then it takes sooooooo looooooong to fill the parchment with a design.
I mixed a small batch of the joconde paste and divided it into seven, colouring each portion with food-gel colouring and white powder colour. I painted rainbow stripes on one parchment sheet, and two designs for the top of the cake on the other sheet. You could pipe the paste, but the thickness of the colour paste when painted on was extremely thin, leaving most of the vanilla sponge uncoloured and delicious as can be seen below. All the colour, with none of the bulk.
The inside of the cake can be whatever you like. This one is filled with two layers of strawberries in a cream-cheese cream, with the offcuts from the sponge being fitted together, jigsaw-style, to make a middle layer. Alternatively, you could make it a mousse or cheesecake or Eton Mess or buttercream – the possibilities are endless – although something that will ‘set’ will help the stability of the cake once it is removed from the mould.
You can make the rainbow pattern any design you like, however the stripes are very easy to match up, which helps to hide the join – see below. This 19cm diameter cake needed a strip of sponge almost 70cm long to form the sides – impossible to bake in a single strip.
A few more tips:
- You can make the sponge any flavour, but I got by far the best results (in terms of colour) from vanilla.
- Chocolate joconde makes the colours very muted and the blue/indigo/violet were almost indistinguishable. Avoid.
- Mixing in some white food colouring (powder) to the Joconde paste made the colours much stronger once cooked. Before baking, they are pale and more pastel in hue. Have faith!
- Make sure the decor paste covers the parchment entirely. Early experiments piping the colours and leaving gaps between resulted in large air pockets forming and spoiling the finished pattern.
- You can get an almost invisible join between the sides and the disc of sponge used for the top if you make sure your filling is almost to the rim and you mitre the edges of the sponges.
- The vanilla cream decoration was piped through a piping bag striped with neat gel colouring.
- Depending on the complexity of your design, you might want to spend time on it a day or two before you need your cake – once complete, it can stay in the freezer until needed.
Joconde décor paste
50g unsalted butter, softened
50g icing sugar
50g egg whites
60g plain flour
rainbow food colours
white food colouring powder
2tbs melted, clarified butter
- Line two 45cm x 30cm (half sheet) baking trays with baking parchment and brush thoroughly with the melted butter. Clarified butter contains no milk solids that might scorch and spoil the colours of the design. Alternatives are cocoa butter or coconut butter.
- Cream the butter and sugar until light and fluffy then gradually add the egg whites, beating continuously.
- Fold in the sifted flour.
- Divide into seven small bowls, 30g in each bowl.
- Mix in the food colouring to each bowl until the desired shade is achieved. I also added about half a teaspoon of white colouring.
- Paint your designs for the sides and top of the cake onto the two sheets of buttered parchment.
- When finished, put into the freezer until required.
180g egg whites, at room temperature
25g granulated sugar
225g ground almonds
225g icing sugar, sifted
6 large eggs
2tsp vanilla extract
80g plain flour
85g clarified butter, melted
- Preheat the oven to 220°C, 200°C Fan
- Whisk the egg whites until they form soft peaks.
- Add the granulated sugar and continue whisking until stiff peaks are formed.
- Scrape the meringue mixture into a bowl and cover with cling film to prevent the meringue collapsing, or if you have two mixer bowls, just swap over a clean one.
- Beat the almonds, icing sugar, vanilla and eggs in the bowl for 5 minutes until the mixture is light and fluffy.
- Turn the speed down to low and mix in the flour.
- Gently fold in the meringue mixture using a large spatula.
- Put the melted butter in a small bowl and mix in a cupful of the sponge batter. Pour this back into the mixing bowl and gently fold into the rest of batter.
- Retrieve your Joconde paste designs from the freezer and lay them into your baking trays.
- Divide the mixture evenly between the tins and smooth over. Pay special attention to the corners, where it is easy to accidentally leave the batter a little on the thin side.
- Bake for 5-7 minutes, until the sponges are cooked and springy to the touch and have shrunk away from the edges of the pan.
- Turn out by laying a tea towel onto a sheet of parchment, then flip the baking tray over onto the cloth. Peel off the paper to reveal the pattern, and lay it lightly on top of the sponge. Leave to cool.
- When cooled, cut strips of sponge to line the sides of the cake tin, ensuring the pattern is facing outwards against the sides of the tin. Cut a circle of sponge to line the base and lay it patterned-side down, in the bottom of the tin. Cut a second circle to make the top of the cake and set aside.
- Fill with the filling of your choice. Use the sponge cake offcuts to make a middle layer of cake if liked.
- Trim the edges of the sponge ‘lid’ and the sponge sides and join together.
- Lay a chopping board on the top of the cake to press it lightly and chill for an hour or two to firm up.
- Remove from the tin and transfer to your serving plate.
- Garnish as liked.
 No not that one. The one from the Hillaire Belloc poem: (Matilda told such Dreadful Lies) It made one Gasp and Stretch one’s Eyes!