To make my 3 layers I used my avocado chocolate cake recipe and baked the whole batch in a 9"x 9" square tin. I've advised a 7"x 7" in the ingredients list. I'll show you why in a minute...

After cooling, trim so the height of the 3 layers stacked is the same as the width of each layer. Mine was 6"high taking jnto account the buttercream extra height allowance so I trimmed the layers to 6" squares. I knew here I had far too much cake so instead of squaring the whole layer I only cut 2 side. You should square every side. Again, you'll see why in a minute...

Cover the whole cake with a thin layer of buttercream. This is your crumb coat. It doesn't have to be neat. We're putting another coat on top

Add you second coat of buttercream to the cake and smooth off. Hang your first recangle of black icing and smooth down and trim any excess

Add the next piece or pieces, smooth, trim down, done! That was easier than you thought wasn't it!

Use the back of a knife to mark the Rubik's squares

Now the fun part. We have 5 faces of coloured squares to stick on! 9 squares in a grid × 5 sides to decorate = 45 squares. In 6 different colours this means you need to cut 7 squares from 3 colours and 8 squares of the other 3 colours. Measure each space on the Rubik's cube and make your coloured squares half a cm smaller

And with the final colour you're done! Ignoring baking and cooling time, decorating one cake took me around 2 and a half hours

Add your candles and any other decorations and prepare for everyone to be impressed!