Weigh out all the dry ingredients in a large sized bowl.
Mix well – best with the electric whisk on slow.
Set your oven to 180°C ordinary – best not to use the fan setting for cakes
Weigh out all the wet ingredients into a jug – zeroing after each addition, and whisk.
Grease and line your pan. Greased greaseproof paper on the bottom – you can cover the separators I guess to make it easier to get the cake oblongs out – I’m going to try that next time. Put just the middle separator in at first – not the other two.
When the oven is up to temperature – tip all the wet ingredients into the dry ones and whisk – a bit slow at first, but as quickly as you can ramp up to full speed and give it a good whisking – incorporating as much air as quickly as possible – a couple of minutes max though.
Divide the mixture in two. In one add enough food colouring (not cochineal/E120 as it's not vegan) to get a pink colour, and enough yellow in the other to get a nice yellow colour. Give each a quick mix starting with the yellow.
Fill one side with the yellow cake mixture approximately 3/4 full = 460g
Then pour the pink mixture in the other side the same - also 3/4 full = 460g. The tin with one separator and mixture in both sides should weigh 1134g
Carefully insert the other 2 separators so you have four long troughs each 3/4 full of batter.
Give it a little shake back and forth in the direction of the troughs – this is so there will be slightly less batter in the middle to give a more uniform and even rise.
Bake for 40 minutes minimum and check after 40 minutes with a cake tester to see how it’s doing – probably needs 45-50 mins as it needs to be fully cooked.
Allow to cool for at least 20 minutes – then cut the cake down to the top of the dividers so it’s completely flat. You can use this cake with some jam in between like a Victoria sponge. Then cut all the way round the outside edge to release the cake – use a plastic knife or spatula so as not to damage the cake tin.
Carefully remove the 4 cakes together from the tray.
Remove the greaseproof paper, and separate the 4 cake oblongs.
Mix a little water with the jam, heat a little in the microwave, and blend into a smooth slightly runny liquid with stick blender.
Lay the oblongs 2 pink & 2 yellow next to each other. Brush the top surface with the jam. Rotate 2 of the oblongs so they are on top – so 2 pinks on top and 2 yellows on bottom – split down the middle where they are cut, and lay them flat again, turning one pair round the other way – it should then be pink/yellow/pink/yellow. Paint with the jam again. Rotate one pair onto the other pair to create the traditional pattern of pink diagonally opposite pink and the same with the yellow. Pat/gently press the four oblongs together into a nice solid square shape.
Roll out the marzipan on a cool surface dusted with icing sugar. Use the tin as a measure – marzipan the same length as the oblongs, but twice the width of the tin, plus almost the width of one of oblongs – to give a joining flap. Best to roll it out bigger than you need and then cut the shape you want – otherwise a 450-475g pack is too thick – needs to be quite thin.
Paint the marzipan with the jam, but leave a strip 1/4 the width of a block at each short end.
Place block on jam – just where the jam starts. Press down gently to get it to mate with the jam. And with a palette knife, make a very slight dent where the first fold will be on the other side of the block from the flap.
Using the palette knife, lift the marzipan and cake and rotate through 90° being careful not to move it on the jam. Again press down gently and repeat the process.
On the last one you will need to bend the marzipan lip out of the way, so do it near the edge of the surface you are working on.
The best way I have found so far is to use a crimper, or a couple of straight edges to press the 2 flaps together so it sticks out at 45° to the 2 sides, and then either crimp by hand or with a couple of straight edges, and then trim quite close with a pair of scissors.