Prepare by making sure your blender is entirely dry. Next, add the granulated sugar and cornstarch to the blender; the cornstarch will help maintain the sugar's dryness and stop it from clumping.

Blend the ingredients at high speed for 30 to 60 seconds until the sugar transforms into a fine, fluffy powder. Stop occasionally to scrape down the sides for even blending.

Sift powdered sugar to remove lumps. Store the finished product in an airtight container in a cool, dry place.