Bring first 3 ingredients to a boil in a 2-qt. saucepan over medium heat, whisking constantly; boil, whisking constantly, 1 minute. Remove from heat; gradually whisk in powdered sugar and rum until smooth. Whisk gently 3 to 5 minutes or until mixture begins to cool and thickens slightly. Use immediately.
simple and quick! be sure to use asap when glazing your sweet treats! also- if no evaporated milk is on hand, use 1/2 and 1/2