when i am trying to make a cake i always run out or don't have icing.. This is a go to icing for me.. And Its fast and easy...You can also refrigerate this up to 5 days as long as you have it covered tightly.
In a large bowl, beat the yolks with an electric mixer until light in color; reserve.
Combine the sugar and corn syrup in a small saucepan (preferably nonstick) over med heat , stirring constantly, until the sugar dissolves and the syrup comes to a rolling boil. Transfer the syrup to a heat proof bowl to stop cooking. Pour a small amount of syrup in the yolks and begin beating with the electric mixer. Pour the remaining corn syrup into mixture in a steady stream. Continue beating until completely cool and fluffy, About 4-5 minutes.
Gradually beat the butter and vanilla til the icing is light and fluffy; about 2-3 minutes.