Sift the powdered sugar into a medium mixing bowl to remove lumps.
Add milk and mix until smooth. The mixture will be thick at this stage.
Stir in the corn syrup and vanilla extract, mixing until fully incorporated.
Adjust the consistency by adding more milk (a few drops at a time) for thinner icing or more powdered sugar for thicker icing.
If using food coloring, divide the icing into bowls and mix in gel food coloring until desired color is reached.
Use immediately for decorating, or store covered to prevent drying out.