(easiest with chocolate & vanilla sponge)
1. Bake as many layers as needed, I had 2 but can do many more.
2. Measure diameter of cake and draw onto baking paper. Divide up the circle into equal sections. I divided mine into 3, so when the cake is cut into a slice, you can see 3 squares of colour.
3. Cut circles out of baking paper, and lay on top of cake and cut out carefully with a sharp knife. (I greased mine so it stuck a little bit, helping to make the cutting more accurate) Once all the circles of cake are cut, start putting them back together but alternating the sponges.
4. Spread a layer of butter icing on (or jam, whatever. I cheated and used Betty Crocker) and repeat step 3 again with the second layer of cake.
5. Cover cake in icing (whatever you choose) making sure you can't see what's hiding beneath!
6. Decorate as usual. I made a stencil so there was a huge glittery 60 on top :)