Icing sugar, also called icing sugar, is a very fine powder commonly used to make cake icing. Additionally, you can add icing sugar to icing that is too thin to thicken its consistency. Icing sugar has an anti-clumping agent mixed in that prevents it from causing lumps when you add it to icing. However, if you are out of icing sugar and still need to thicken icing, you can make a substitute with common ingredients.
Combine cornstarch and granulated white sugar in a food processor. This combination mimics the sweetness and thickening properties of icing sugar.
Turn the food processor on high for two minutes to mix the sugar and cornstarch into a fine powder.
Allow the mixture to set in the food processor for one minute before opening. This allows the sugar dust to settle, avoiding a sticky mess on your countertop.
Pour the icing you would like to thicken into a small bowl.
Add 1 tbsp of the sugar mixture to the icing and stir with a spoon until thoroughly combined.
Allow the icing to set for five minutes and test its thickness by scooping up a spoonful and letting it drip back into the bowl.
Continue adding 1 tbsp of the mixture to the icing until it has reached your desired thickness.
Store any unused mixture in a plastic sandwich bag in a cool, dark place such as your cupboard.
Never pour cornstarch directly into icing as it will cause hard, dough-like lumps.