how to thicken cake glaze
Add Thickeners. Adding any type of starch to a glaze will thicken it quickly. For every 1 cup of glaze, mix together 1 tablespoon each of cornstarch and cool water or other cooking liquid. Whisk this mixture into the glaze and simmer it, stirring often, until the sauce thickens. Use the same technique with tapioca starch or arrowroot powder for a super glossy glaze.