Place the butter in a large mixing bowl with the caster sugar.
Beat until light and fluffy with a wooden spoon.
Gradually beat in the egg until well mixed, then slowly add the flour.
Use your hands to bring the mixture together to a stiff dough.
Roll into a ball and chill for 30 minutes.
Preheat the oven to 180°C / 350°F / Gas mark 4.
Line two baking trays with greaseproof paper and set aside.
Roll out the dough on a lightly flour dusted surface until it's the thickness of a €1 coin.
Using an oval cutter (or an egg-shaped template) cut out the biscuits, using rolled out trimmings to make more as you go.
Place on baking trays and bake in the oven for 6-10 minutes, depending on size, until just golden brown.
Allow to cool for 5 minutes before removing from the baking tray to cool completely.
To decorate, make up the icing as directed and divide between 3-4 bowls adding a little food colouring to each bowl.
Place the mixtures into piping bags and decorate the biscuits you wish and have the children help with sprinkles or sweets and funny faces too.