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.
Notes
This homemade powdered sugar can be used as a substitute for store-bought powdered sugar in various recipes such as frostings, glazes, and dusting desserts. Adjust the quantity as needed to match the amount required in your specific recipe.
When using it in a baking recipe that's a little more specific like a cookie, I like to sift my homemade powdered sugar first because it's a bit heavier than store-bought powdered sugar to ensure the accuracy in the recipe.