I have not purchased confectioner’s sugar for at least 15 years. I make it fresh when I need it and never have it get old or cakey in the cupboard.
If you do want enough to store, add 1 teaspoon cornstarch per 1 cup sugar in the blender.
Using a clean glass blender (will scratch plastic), add one cup sugar. Cover and pulse until fine and powdery. Pour through a seive into a container and use right away.
As an alternate, pulse about 30 seconds for superfine sugar. This is a perfect alternate to granulated sugar for whipped cream, frosting, cheesecake, angelfood cake, and so on.
Use your new non GMO sugar for making confectioner’s or powdered sugar.