What is Castor Sugar?

Castor sugar is a very finely wrought sugar product. It isn't powdered sugar (sugar to which anti-clumping agents like cornstarch have been added). It's a granulated sugar, but the granules are very tiny. In the U.S., castor sugar is often called superfine sugar. If you aren't a sugar purist (and I'm so not), you can approximate castor (or superfine) sugar by processing regular old granulated