01 - In a medium bowl, mix sifted powdered sugar, milk or water, corn syrup, and vanilla extract if using until smooth and glossy.
02 - Whisk the mixture; if too thick for piping, gradually add milk or water by 1/2 teaspoon increments until desired consistency is achieved.
03 - For firmer icing, beat in egg white or meringue powder with water until stiff peaks form.
04 - Divide icing into smaller bowls and incorporate gel food coloring for vibrant hues as desired.
05 - Transfer colored icing to piping bags fitted with fine tips suitable for detailed decoration.
06 - Apply icing to cooled gingerbread cookies and allow to dry completely for 1–2 hours before stacking or packaging.