Spiral cake with marbled sponge – or cake and maths

I was doodling spirals, as you do, and wondered how I’d go about decorating a geometric spiral cake… after much more doodling and some time creating a pattern in Adobe Illustrator, this cake is the result.

I thought perhaps a plain sponge might be a bit of a let down after having such a graphic outer layer, so this is a vanilla and lemon verbena sponge and chocolate and orange sponge marbled layer cake. You know me by now – I either go for a real plain but intensely classic and tricky perfect bake or I have to fiddle about with the flavours.

Notes

If you haven’t got lemon verbena, just add plain milk to the sponge and then add in one half teaspoon of lemon juice. (Skip the warming and infusion notes)

You can use either the plain spiral and print it out to your own size

Or you can use the PDF I’ve set up which will print out two pages of A4 which can be cut and pasted together to give an exact 21cm diameter pattern, which is right for a 20cm cake tin (plus buttercream and icing layers)

How I worked out the spiral

I took the diameter of the cake tin and added 1 cm to account for the icing and buttercream that would be layered on

I drew two radius lines from the centre of the circle to the circumference, 36° apart. This 36° angle gives me ten arcs in the spiral, an even five each of two colours. A circle is 360° in total, so 360 divided by ten is 36

Using each radius line as a diameter, I drew two smaller circles inside the radius of the larger circle

Where these two circles intersect each other and the larger circle gives me the arc that I want. This is the red shaded area.

I know that this one arc can de duplicated ten times to produce the spiral I want as it’s been set up using geometry to get a perfect result.

Using the template

I’ve given you a pdf template below that will make up a spiral for a 20cm cake (it is slightly wider – 21cm to accommodate the buttercream). This will not fit properly for printing on a single A4 sheet, so you need both and to cut and glue the sides together.

SpiralCakeTemplate_InkSugarSpice_2016

Equipment

Cutting board/surface
Sharp craft knife – I use a Swann-Morton scalpel (used one ever since art school and I even use these for slashing my bread. Be careful – they are designed to cut flesh: the sterilised versions are used by surgeons! However, I don’t think you can beat them)
Card – A4 piece
Print out of the swirl template I’ve provided for you
2 20cm cake tins, preferably loose bottomed or springform
Baking parchment/greaseproof paper
A small saucepan or a small microwaveable bowl
Two bowls
Skewer
Spoons, spatulas, crank handle palette knife (preferable) or plain palette knife
Measuring jug (small scale) and set of weighing scales

Ingredients – sponge

Eggs – 2 large
Unsalted butter, softened – 100g
Baking margarine – 100g
Caster sugar – 200g (I used golden for this but ‘normal’ will do)
Plain flour – 185g
Cocoa – 15g
Baking powder – 1 teaspoon
Milk – 50 ml (of which you’ll only actually use 20ml)
Lemon verbena leaves – 5 or 6 leaves
Orange juice – 20 ml

Ingredients – chocolate buttercream

Unsalted, softened butter – 200g
Icing sugar – about 400g
Hot chocolate powder – about 40g
Milk – about 20 – 30 ml

Ingredients – icing

Red fondant icing, a shop bought pack or homemade – you will need about 150g
White fondant icing, a shop bought pack or homemade – you will need about 150g
Icing sugar to keep the surfaces dusted

Method – cakes

Put the oven on to 170C fan / 180C conventional
Make sure your two cake tins are greased and lined/floured
Gently warm the milk and the lemon verbena leaves in the smallest saucepan you have over a low heat. Swirl the leaves around and heat until it is just blood temperature – you’ll be able to dip your finger in and it feel neither hot nor cold. Take off the heat and leave to infuse for a few minutes
Put 50g of butter, 50g of margarine and 100g of caster sugar in a bowl
Cream the fat and sugars together
Add one egg and then sift in 85g of the flour, cocoa and 1/2 teaspoon of baking powder and mix together
Add the orange juice (you may not need quite all the 20ml) until the batter is a typical cake consistency
Put the chocolate and orange batter to one side
Put 50g of butter, 50g of margarine and 100g of caster sugar in the second bowl
Cream the fat and sugars together
Add one egg and then sift in 100g of the flour and 1/2 teaspoon of baking powder and mix together
Measure out 20ml of the infused milk (discarding the leaves) and add it to the batter (as before you may not need quite all of it, so my tip is to put about 10ml in, mix, and then judge the consistency adding the rest only if required)
Take both baking tins and splodge spoonfuls of the lemon verbena sponge batter into both tins, trying to even the amount out (Fig. 1)
Fig. 1
You can test whether your tins are of equal weight (and therefore holding equal batter) by ‘zeroing’ your digital scales and putting one tin on. Note the weight. Take off the first tin and put the second on – is it the same? If it’s out by a lot transfer a little of the batter from the heavier tin and weight them both again
Now splodge in the chocolate and orange batter in the same way, but try to fill in the gaps you’ve left with the lemon verbena batter (Fig. 2)
Fig. 2
Weight the two tins again to see if they’re level
Smooth over the batters in both tins to try and get an even surface – try not to smudge the two batters together too much. However the truth is you’re only smooshing the very top layer and as this will get browned in the over and you won’t see it once the cake is made (Fig. 3)
Fig. 3
Tap the two tins on the counter
Bake for about 25 minutes until springy to the touch and/or a skewer comes out clean
Leave to cool in the tins

Method – buttercream

Beat the butter, hot chocolate powder and icing sugar together together, adding a little splash of milk as you go to alter the consistency. Whip for a good few minutes as this will ensure it is light and airy

Method – construction

Once cooled, sandwich the two sponges together with the buttercream (Fig. 4)
Fig. 4
Spread the buttercream on the top and sides of the cake and smooth it over as flat as possible (Fig. 5)
Fig. 5
Cut out the template
Poke a small hole dead centre of the template and lay it on your cake, trying to make it as centrally aligned as possible – mark the centre of the cake with the skewer. Mark the edges of the cake at the ten points on the circumference and then take off the template
Dust the surface you’re working on heavily with icing sugar
Note of warning!! Make sure you do not turn any of the template pieces upside down or that piece of fondant won’t fit.
Roll out one colour of the fondant larger than the template
Lay the template on the fondant
Carefully cut out the five arcs – this will also cut your template (this is OK! You could cut out just one arc from the template and use that to cut five from the icing anyway)
Put the five arcs to one side and roll out the other fondant
Take just one of the arcs (this is easier now) and use it to cut out five in this second colour fondant (Fig. 6)
Fig. 6
Take one arc of fondant (doesn’t matter which colour) and use the template or the picture of the spiral here as a guide to ensure you’re laying it the right way – the fatter, more oblique end goes nearer the centre and the thinner, acute end of the arc goes on the edge of the cake
Align the point of the arc to the hole you poked in the centre of the cake and align the piece of fondant so that the ‘tail’ end sweeps and meets the edge of the cake
Take one arc from the other colour and lay it next to the first arc on the cake – they must touch. Make sure you lay the point to the centre of the cake
Repeat until all the arcs are laid and the top is complete (Fig. 7)
Fig. 7
To complete the sides, take a scrap piece of paper (from the template you’ve just mauled) and measure the length of one colour along the side of the cake
Cut a rectangle in the paper so that the long edge matches this section of fondant on the edge and the short side equals the height of the cake
Using this paper template cut out five rectangles of fondant icing in each of the two colours
Press these fondant rectangles on the sides of the cake
Pinch together the edges and smooth with either a finger tip dipped in water or a moulding tool if you have one
That should be it – you may want to either give the cake a spritz of water from a sprayer or use a clean pastry brush to give it a ‘wash’ with some water. This cleans it up, dissolves any leftover icing sugar powder and helps bind the edges together