Put the butter and icing sugar into a large mixing bowl. Use an electric mixer to cream the butter and icing sugar together, until pale and fluffy. Should take about 5 minutes
Add vanilla extract and beat until incorporated. Add in your food colouring and mix to the colour you want.
For the letters, I cheated and used all ready made roll out icing. I used alphabet cutters to cut out the letters I wanted
Then I add them to the top of my cake to spell out my message. It says 'I AM GRADUATING'