More cake. Seriously. (hidden design cake)

Look, I don't only make cake. I cook other things too. But I just don't blog them - they're too dull. Maybe I should find more interesting dinners, or maybe dull, safe, easy dinners are just fine when you are also toddler wrangling. Celebration cakes, on the other hand, are infrequent and infinitely more exciting than Yet More Pasta. This one was so exciting I even had a practice run. Oooh.

Inspiration came from this Tablespoon recipe for Rainbow Tie Dye Surprise Cake. Swiftly followed by "ow, my eyes!" "I need to spend HOW much on gel colours?" and "packet cake mix - meh". So it was then tempered down to UK standards (and ingredients) by this BBC Good Food recipe for a Hidden Heart Cake. The plan was to follow the HH recipe but partify the innards with different colours.

There's no point in telling the whole story of the practice run and the main event, so I'll just try to get a sensible recipe and all the tips down for my (and maybe others') future reference. As an overview, you make one coloured cake, cool and slice it, cut a design out of the slices with a biscuit cutter, then place the cutouts in the centre of a plain cake which you bake around them.

The basic foundation is the N-egg sponge. You take your eggs, weigh them, and then use the same amount of soft unsalted butter, golden caster sugar and self raising flour - it means you can actually make it work with whatever eggs you have to hand, small or large. I used a 3-large-egg (roughly 180g) sponge for the inner design and 4+ large eggs (~260g - see, a different source of eggs and a different size) for the main cake (see tips below).

I used a creaming method to make the cakes: cream the butter and sugar really well until pale and smooth, then whizz in the eggs (and vanilla, if using), and finally fold in the flour.

For the first cake, at this point I split the mixture into 4 to add the colours. I used 2 Sugarflair colours, Royal Blue and Melon, plus a Dr Oetker red, given to me by a friend. I remembered from reading baking forums or comments on recipes that the Dr Oetker gel colours are not the same sort of thing as the "pro" gels like Sugarflair, being weaker, and boy was that the case. The blue especially was very vivid, and the red was not vivid at all. In my cake mix (remember, a quarter of a 3-egg sponge), I used almost all of the whole 10g tube of red, whereas I used a *tiny* amount (the tip of a teaspoon handle - maybe half a pea-sized amount) of the blue. I was a little (but only a little) more generous with the yellow, and added in a blob of red too to make it more orangey (to stand out from the surrounding plain cake), and then mixed yellow and a tiny smear of blue to make green. (Note: gel colours on eBay are cheaper, e.g. any 3 for £7 as opposed to £3.25 each, but you might also like to support your local cake shop!)

You can see how the colours came out in this slice:

That was pretty much the effect I was hoping for. I didn't go the whole hog (as per the Tablespoon recipe) of piping the colours in a Pollock-esque splatter, but just dropped in teaspoonfuls. Once I had used all the mixtures I dropped the tin flat on the surface a couple of times to settle them all down. For the test cake I used larger spoonfuls and swirled with a skewer but the effect wasn't mixed enough when cut, so the teaspoons are worth the extra time.

Which brings me to the tin. I used a silicone loaf tin, 2lb size (about 9" x 3"), and while this makes the cake easy to release from the tin, the sides do bow out when using a lot of mixture. Not the case at this stage, but definitely a problem for the final cake.

I baked at 140°C (fan oven) for 1h10 and the cake was done perfectly. After 10 mins in the tin I turned it on to a cooling rack and left for a good few hours to cool. I sliced it into 1" slices (depends on your cutter depth) and cut a star out of the centre of each one. The cake was tricky to release from the cutter but luckily it was a nested set of star cutters so I used the next smallest one to poke it out :) I would say you need to think carefully about your shape, and any skinny protrusions will be troublesome. Remember you not only have to cut the shape out and keep it whole, but also place it in the other cake mix and get it evenly surrounded and supported. Also the more cake you use out of the coloured loaf, the less plain cake mix you will need! Round shapes like BBCGF's heart are a great choice.

Phase 2 involved making more plain cake mix, 4 eggs this time. I put a thin layer in the bottom of the tin and then placed the stars in a tight row on top of it (making sure they were in the same order so the swirls matched up - picky, me?). I then used a piping bag with a wide nozzle to get the cake mix down the sides, before piping the last of it on top. Here the bulging sides of the silicone pan were unhelpful as they created more space and meant the mixture did not cover the stars - argh. I actually ended up whizzing an extra egg's worth of sponge together to go on the top, before I realised that there would be enough if I could hold the sides up. This involved getting a bit Heath Robinson with a roasting tin and some folded tinfoil, which upped the cooking time (almost 2 hours)... the mixture overflowed volcanically... anyway, long story short, use a metal tin if you value your sanity.

The other thing, which I have no idea how to control, is that as the cake cooked (or perhaps during my piping of cake mix, or during my fiddling with tinfoil) the stars moved, off-centre and upwards. So when I trimmed the cake top for icing, I sliced into the star (see top photo). Nooo! I never thought I would curse a cake for rising! This happened a bit with the practice cake, but not as much. My best suggestion is to use just a very thin layer of plain cake on the bottom and wedge the coloured shapes well down into it, and make sure not to pack one side better than the other.

With the cake done, I crumb-coated with buttercream (75g butter, 175g icing sugar, tbsp milk) and then coated with plain white fondant and stars cut from coloured fondant. Another learning point here: when moistening fondant shapes to apply onto the white, use barely any water to avoid coloured dribbles. A ribbon around the bottom finished it off.

So, main cake complete but I felt guilty about the amount of offcut coloured cake. Not that it wouldn't get eaten, but it seemed a shame. Another 3-egg sponge mix was divided between 12 muffin cases with a chunk of offcut in each. As it was getting late I made the sponge with an all-in-one method (no creaming, just whizz everything together) and it was perfectly tasty, just a bit more crunchy on the top. I also stirred in a pack of sprinkles to try for a 'funfetti' effect. It was more successful than last time (I used Dr Oetker sprinkles this time). More fondant stars stuck with the last of the buttercream completed the look.

So, there we go. Been there, done that, not rushing to repeat the feat but still quite pleased with it despite my wonky stars. But blogging the experience just in case I change my mind!