This type of cake is really simple but effective and always goes down well with kids and grown ups alike. But there are a still a few things that can go wrong if you're not in the know, so here I give you my top tips for making a Smarties Rainbow cake, from the batter right through to what to do with those leftover Smarties...
The Rainbow Sponge
Well, the rainbow cake bit is optional. If you want it to be a rainbow cake, then when you make your sponge batter (which should be vanilla/lemon/anything pale in colour), separate it into different bowls, weighing the entire amount first then separating into equal amounts. Use a gel or paste food colouring like ProGel or Sugarflair so your batter doesn't go runny but you get a really nice bright colour. If you don't want to do six layers, just Red, Yellow, Green & Blue do the trick nicely (as I did for this one).
Bake the layers of sponge in the same size tins. If you need to bake a couple of layers at a time, then let them cool, turn out, then regrease and bake the next lot of batter. The batter will keep fine in the meantime and it'll be far easier to get a neat, structurally sound cake. Bake until a skewer inserted in the middle comes out clean, and not a minute longer, for a nice moist, fluffy cake!
Once baked, use a good bread knife or cake leveller to slice off the rounded tops so the layers are perfectly flat. If you're doing 6 or 7 layers, pop 3 dowels in a triangle shape through the top of entire cake to keep it stable so the layers don't slide around. Cut them off flush with the top of the cake. I speak from experience of having to pull in at Bingley Home Bargains to buy emergency straws to salvage a very jammy, buttercreamy drip cake. Not a fun time.
Use a crusting buttercream (which is what normal UK buttercream is) and make quite a lot of it. I'd use around 500g butter and 1kg icing sugar to be on the safe side. You can use the remainder for other cakes, or to eat over the sink with a spoon after a really bad day. Use your buttercream to sandwich each layer, and then do your 'crumb coat' - this means slathering a thin layer of buttercream all over the cake to catch all the crumbs in it and refrigerating for an hour. Don't worry if it looks awful, it's supposed to. Then when it's dry to touch get it back out and do a thicker layer of buttercream all over. It's going to be covered in Smarties, so don't spend much time making it look neat.
Let your buttercream covered cake sit for a couple of hours on the counter till the buttercream starts drying. You don't want it completely dry and crusted, just a little bit. Enough so the Smarties won't bleed into it, but still sticky enough that they actually stick to the cake. If it's a really hot day, pop it in the fridge for 10 mins instead (or if you're in a rush).
You need at least 4 packets of Smarties. Open them all and sort them into the separate colours in containers. It may help to Duck tape your mouth shut while you do this. Start from the middle of the top, and build each layer outwards. Try to keep them as straight as possible. Push them firmly into the cake but not so far that the buttercream squidges everywhere.
Use the remaining Smarties to feast on at 4.45pm when everyone is yelling at you, or bribe your kids to put their shoes on.
Ta-daaah! Your Rainbow smarties cake is finished. Serve within 24 hours so the Smarties don't bleed colour everywhere! Lastly, DO NOT PUT THIS CAKE IN THE FRIDGE! It will mean the Smarties do leak their colour due to the moisture.
If this all still sounds like way too much work to you, get in touch with me using the Contact form to order your Smarties Rainbow cake from me!
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