Preheat the oven to gas mark 4 or 180 degrees.
Cream together the butter and the sugar in a bowl (I usually leave the butter out of the fridge to soften before I bake).
Add the two eggs and flour and fold until you have a smooth cake mixture.
Carefully spoon the mixture into 12 fairy cake cases in a shallow baking tin. (Optional - add a few of the 100's and 1000's to the mixture and the top of the bake for a little extra colour.)
Bake for 20 minutes or until golden, then leave to cool on a wire rack.
To make your icing, add a little tepid water to the icing sugar and stir until it has a thick consistency.
If it's too runny, add a little more icing sugar, if it's unspreadable, add a drop more water.
Spread onto the top of the cakes in a circular motion with a knife and sprinkle with 100's and 1000's.