1Preheat the oven to 180C/160C Fan/Gas 4. Grease and line 3 x 20cm round cake tins.
2For the first batch of cake layers, put 187g of each of the Stork, caster sugar and flour in a large bowl. Add 1tsp vanilla and 3 eggs, then beat with an electric mixer until smooth.
3Divide the mixture between 3 bowls. Add about 1tsp of blue colouring to the first, mixing in well to get a uniform shade. Repeat with the other bowls, to get green and orange mixtures.
4Spoon each mixture into a separate tin and bake for 18-25 mins, until risen and springy to the touch.
5Remove from the oven. Leave the cakes to cool in the tins for 10 mins, then gently turn out onto a wire rack to cool completely, removing the baking paper.
6Repeat Steps 2-5 to make the second batch of 3 cakes, using the remaining 3 colours.
7To make vanilla icing, put the Stork into a large mixing bowl. Sift the icing sugar into the bowl, add the vanilla extract, then whisk everything together until light and fluffy.
8Use a cake leveller or sharp, serrated knife to cut off the tops of the cakes so each one is flat and even. Set aside one cake, then use an 8-9cm plain round cookie cutter to remove the centre from each of the remaining 5 cakes so they are ring-shaped. Take care to do this accurately, so the holes will line up neatly when the cakes are stacked. (Discard any excess cake or freeze to use in another recipe.)
9Arrange your first ring on a cake stand or serving plate, gently spread with a thin layer of vanilla icing. Stack another cake ring on top, carefully lining up the centre holes and carefully spread with more icing. Repeat with the remaining cake rings until you have a stack of 5.
10Fill the centre ‘well’ with the sweets, then place the final (whole) cake on top.
11Put 3tbsp of the icing in a piping bag with a plain nozzle, then set aside. Spread the remaining icing all over the top and sides of the cake. For a really smooth result, run a warm palette knife over the icing to finish.
12Use the piping bag to create a decorative border around the top of the cake. Decorate with sprinkles to serve. The cake will keep for up to 3 days.