1. Line your bun tin with paper bun cases.
2. Make the water icing, cover with cling film and save till later.
3. Break the eggs into a clean jug and beat well.
4. Weigh and measure all ingredients.
5. Pre-heat the oven to 175°C (Gas Mark 3).
6. Place the soft margarine and caster sugar into a large clean mixing bowl.
7. Using a hand-held electric whisk, whisk together until light and fluffy and is pale in color.
8. Scrape down the sides of the bowl from time to time.
9. Whisk at a high speed and gradually add the beaten eggs a little at a time.
10. When all the egg has been incorporated, add a few drops of vanilla extract for flavor.
11. Sieve the flour into the bowl and fold in using a large metal spoon or spatula.
12. Divide your mixture between the paper bun cases, filling them to about ¾ full.
13. Place in the centre of your pre-heated oven and bake for 18-20 minutes until the cakes are well risen, light golden brown and slightly firm to touch.
14. Remove the fairy cakes from the oven and allow to cool on a cooling rack.
15. When completely cold, spread a little water icing over the centre of each cake – you could use a spoon or small knife for this but you may find a small paper piping bag is more user-friendly. You can use different colors of icing.