Preheat the oven to 180˚C (160˚C fan assisted, 350˚F gas)
Line 12 cupcake tins with the Muffin Cases. Put the vegetable fat and sugar in a bowl with the milk and Vanilla and whisk until well blended and creamy. Whisk in the eggs.
Sift the flour and salt on top and carefully mix together until well blended.
Divide the mixture equally between 3 bowls. Add 7g (1/4oz) Blue gel to one, 25-30 drops to another, and 10 drops to the third. Mix each portion carefully to make 3 different blue shades.
Spoon the boldest blue mixture equally between the cases (we used approx. 20g/ ¾ oz coloured cake mix per layer), and smooth to cover the bottom of each case evenly. Working your way from bold to pale, spoon the remaining 2 shades of blue mix, in layers on top of each other, carefully spreading out each layer to cover the one below. Smooth the tops.
Bake for 22-25 minutes until slightly risen, lightly golden, and just firm to the touch. Cool for 5 minutes then transfer to a wire rack to cool completely.
To decorate, sieve 225g (8oz) the icing sugar into a bowl and add the Vanilla. Stir in 25-30ml (5-6 tsp) warm water to make a thick, spreadable icing. Use to cover the top of each cake, spreading the icing to reach the edges of the cases. Leave for about 30 minutes to set.
Meanwhile, sieve the remaining icing sugar, and divide into 6 equal portions. Add a few drops of Food Colour Gel and a few drops warm water to each to make bold shades – we used: 12 drops Red; 15 drops Yellow; 15 drops Black; 15 drops Blue; 10 drops Green and 3 drops Pink.
Place the cakes on a large board, or cover the work surface with kitchen paper and put the cakes on top. Working with one colour at a time, using a teaspoon, drip and drizzle the coloured icing in random patterns on top of each cake. Repeat the process with the other colours. For a more controlled design, load the individual icings into small, uncut piping bags. Snip off the end and then drizzle the icing over the cakes.
Leave the cakes to set for a further 20 minutes before serving. Your colourful cupcakes are now ready to impress and enjoy!