Preheat the oven to 180 degrees C (160 degrees C Fan, Gas Mark 4). Line the bottom and sides of five, loose bottomed 20cm (8 inch) diameter Victoria sandwich tins with baking parchment.
In a large, grease-free bowl, whisk the egg whites until stiff (for best results use a stand mixer with whisk attachment). Add the Cream of Tartar, half of the sugar and the Natural Vanilla Extract. Whisk until thick and glossy.
Sift in the flour and remaining sugar into the mixture in 4 batches, folding in gently after each addition, until well combined.
Divide the mixture equally between 5 bowls. Add a Gel Food Colour to each bowl to achieve desired colour level. Carefully fold in the Gel Food Colour and spoon the mixture into the tins. Green: 20g (10ml, 2 tsp or 1 tube), Blue: 15g (15ml, 1 tbsp or 1.5 tubes), Yellow: 5g (5ml, 1 tsp or half a tube), Red: 3.5g (3.5ml, 1.5 tsp), Red to make pink: 20 drops (1g)
Smooth the tops and bake on the middle shelf in the over for 14 minutes until just firm to the touch and very lightly browned. Carefully turn on to a wire rack to cool completely.
To serve, place the butter in a mixing bowl and gradually sieve in the icing sugar. Stir in the Natural Vanilla Extract and mix in the soft cheese. Mix well to make a smooth, creamy, spreadable filling. Spread 4 layers of sponge with sufficient filling to just cover and sandwich together. Dust with icing sugar just before serving.
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