Besides licking the spoon (cook's privilege).
A good use for left over frosting is to spread on graham crackers and make a sandwich of frosted grahams. The first day, the grahams are fresh and crunchy. The second day (after wrapping in plastic or a zip loc bag) the frosting has softened the graham and it becomes decadent.
Served with milk, it is very high on the scale of ultimate pleasures.