To check the frosting for the right consistency, use a spoon to scoop up the frosting. Hold the spoon about a foot high above the bowl. Turn the spoon on its side and watch the frosting fall from the spoon. If the frosting falls in a consistent, ribbon-like pattern, the frosting is ready. If the frosting is too thick and falls in clumps, add half teaspoon of milk and whisk again. If the frosting runs easily off the spoon, add another 1/2 cup of confectioner's sugar and whisk again.