Melt the softened unslated butter in the microwave for 30 sec
Sieve the icing sugar into a mixing bowl
Pourthe butter over it and mix well
Add the cream cheese
Using a toothpaste add 2 drops of black food colouring and with another toothpick, add 1 drop of ivory food colouring - they mix to give a spooky and slimy grey colour to the frosting
Blend into a smooth paste with a hand blender for almost 4 minutes or until the mixture is smooth and the sugar granules are totally mixed into the butter and cream cheese
To decorate the cake I only used a small amount and after my nephews had a go at decorating I slathered on the remaining slime all over the cake slab - made for a very happy 2 year old ;)
Of you would rather not use up the whole buttercream, simply change the colour to anything you fancy and freeze - keeps for 3 weeks in an airtight box in the freezer
To use thaw overnight in the refrigerator and blend for minutes to get the same texture again
Once thawed use it all up, do not refreeze