In a high-speed blender or food processor, combine the granulated sugar and cornstarch.

Blend or process on high speed until the mixture turns into a fine powder.

Stop the blender occasionally to scrape any powder from the sides and ensure that all the sugar is evenly processed.

Once the mixture has a powdery consistency, transfer it to an airtight container.

Store the powdered sugar in an airtight container at room temperature until ready to use.