Combine sugar, water, corn syrup, and salt in a saucepan and stir the mixture until well blended.
Step 2
Boil slowly without stirring until mixture spins a long thread when a little is dropped from a spoon.
Step 3
In a large bowl, beat egg whites until they are stiff but still moist. Pour hot syrup slowly over egg whites while beating.
Step 4
Continue until mixture is very fluffy and will hold its shape.
Step 5
Add vanilla extract and beat until blended.
Step 6
If icing does not seem stiff enough, beat in two or three tablespoons confectioner’s sugar, one tablespoon at a time, until it’s stiff enough to hold its shape. Spread on the cake.