Jo Wheatley's rainbow vanilla sponge recipe

Jo Wheatley's rainbow vanilla sponge was designed especially for The Rainbow Trust's fundraising initiative The Big Hour Cake Sale. 

Jo says: 'The work Rainbow Trust does to support families of children with a life threatening or terminal illness is immeasurable. With three amazing boys myself I can’t even begin to imagine how hard it must be when one of your children is so seriously ill. It is so important that we all do our bit and so this year I am supporting The Big Hour Cake Sale for Rainbow Trust.' With a gorgeous buttery vanilla sponge and soft sweet buttercream we are sure this could raise some pennies and some smiles!

Ingredients

• 225g margarine or unsalted
• butter, softened
• 225g caster sugar
• 4 large eggs, beaten
• 1 tsp vanilla extract
• 225g self-raising flour
• 2 tbsp full-fat milk

For the decoration:

• 500g icing sugar
• 125g unsalted butter, softened
• 3 tbsp full-fat milk
• 1 tsp vanilla extract
• 2 drops of blue food colouring - nb. retain some uncoloured buttercream for the middle and to secure the icing rainbow
• 2 tbsp strawberry jam
• Smarties
• Dr Oetker Ready to Roll Coloured Regal Ice Icing

Method

1. First make the rainbow. Roll five sausages of different coloured fondant icing, then with a damp finger wet each edge, then 'glue' them together. Use an upturned egg-cup on a piece of parchment to shape the rainbow around. Place a cocktail stick into the bottom of each rainbow sausage, leaving half the stick visible so you can secure the rainbow onto the cake. Leave the rainbow overnight to dry. 
2. Prepare 2 x 20cm sandwich tins. grease and line the bases lined with buttered baking parchment .
3. Preheat the oven to 180°C/350°F/Gas Mark 4.
4. In the bowl of a free-standing mixer, cream the margarine or butter and sugar together until pale, light and fluffy. Gradually add the beaten eggs and vanilla extract. Add the flour and milk and mix until light and fluffy.
5. Divide equally between the prepared sandwich tins, spread level and bake on the middle shelf of the preheated oven for about 22–25 minutes until golden and a skewer comes away clean when inserted into the middle of the cakes.
6. Turn the cakes out of the tins onto a wire cooling rack and leave until cold.
7. To make the buttercream, tip all of the ingredients into the bowl of the free-standing mixer and beat until light and fluffy. Then add a couple of drops of blue food colouring and mix together.
8. Lay one cake layer on a serving plate and pipe or spread the blue buttercream around the edge of the top of the sponge and if you’ve got a steady hand you can do a curved pattern around the edges. Spread the rest of the top of the sponge with strawberry jam. Sandwich the other sponge on top carefully.  Spread the second cake layer with the blue buttercream and finish with a circle of Smarties around the outside edge.
9. Place the rainbow carefully onto the cake by submerging the cocktail sticks into the buttercream and sponge. Then pipe uncoloured buttercream to look like clouds and to hide the join.

Top tip for making this rainbow vanilla sponge cake

You can brighten up the cake even more by using a different coloured icing for the centre. Or you can use two colours, iced in concentric circles, so that you get a striped filling effect with each slice.

How can I dry out my fondant cake topper more quickly?

This rainbow is quite a large cake topper, so it's best to let it dry overnight or even for a couple of days, to harden properly. If you don't have that long, you can try this trick to speed up the drying process a little. If you have an electric oven, lay the topper on a lined baking tray and place it in the oven. Keep the oven off, but put the oven light on, so that the air circulates. If you don't have an oven with a light, you can place the topper under a lamp and next to a fan to recreate the effect.

How can I make clouds with the buttercream frosting?

We used a wide serrated nozzle on a pipping bag to create this cloud-like effect with the uncoloured icing. It's the easiest way to get a pouffy, scrunched up effect. If you want it to look even more cloudlike, you can use a wide, smooth-edged nozzle, to create big smooth puffs. Tamp down the edges so you don't get points on the clouds.

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