Preheat the oven to 180°C/350°F/Gas 4, Gas Mark 4 and put the middle shelf in position. Line the baking tin with baking paper. Put the butter and sugar in a large bowl and cream together until pale and fluffy. Add one egg and half the flour and beat well. Add the remaining eggs and the flour and beat well again. Dollop the mixture into the prepared tin and level with a palette knife.
Bake in the oven for 30 minutes, or until a skewer inserted in the thickest part comes out clean. Remove from the oven and flip upside down onto a wire rack. Lift out of the tin and leave to cool on the wire rack.
Meanwhile, prepare the marzipan. Roll out the marzipan on a well-sugared board to around half a £1 coin thickness. Roll it out to slightly larger than the size of the sponge. Once the cake is cool, peel off the baking paper that it was baked in and turn it right-side up. This top side should now be nice and flat.
Spread the apricot jam over this bottom half and then carefully layer the marzipan over the sponge. This is quite tricky and the marzipan can tear but it is very easy to patch it up. Trim off any excess with scissors. Place the sponge in the fridge for about 30 minutes, or until firm.
Meanwhile, make the buttercream. Put the butter, icing sugar and vanilla in a bowl and whisk until it becomes pale and fluffy. Remove the sponge from the fridge and slice in half horizontally. Spread with the buttercream and sandwich back together. Pop back in the fridge while you prepare the fondant icing.
For the fondant icing, make the icing almost to the packet instructions, they tend to say to add too much water on the packet and you want this icing to be thick enough not to drop off the cake once it has been put on. Divide the icing among three bowls and colour each one with your choice of food colouring.
Remove the cake from the fridge. Have a wire rack ready with baking paper underneath it to catch all the drips. Take a piece of the sponge on a fork and hold the top lightly with your forefinger. This is messy work and very time consuming but the results really do speak for themselves, so it is well worth the perseverance.
Dip the cake into the coloured icing of your choice, dip it right down until the whole thing is covered then place on the wire rack to set.
Repeat with all the sponges. If, as does so often happen, you find your fondant icing is riddled with sponge bits, simply strain the fondant icing to remove them.
While this icing is setting make your Royal icing according to the packet instructions. Again, you can colour this if you want to with the food colouring. Fill a small piping bag fitted with a tiny round nozzle with the icing and pipe decorations on top of the iced cakes. If you don’t want to go to the bother of using Royal icing you can just melt some chocolate and flick it over the top. Leave to harden. These little cakes keep for up to three days. Serve with tea and biscuits.