how does caster sugar work?!
Castor Sugar is sold as Superfine Sugar in the USA. It is a finer grind than granulated sugar but still has crystals as opposed to confectioner's sugar which is a sugar powder. Castor or Superfine sugar is used in making drinks, meringues, sauces and any recipe where you want to be sure the sugar totally dissolves. You can substitute the same amount of granulated sugar for superfine sugar, but place in food processor and grind until it is superfine, not powdered.
Castor sugar is also sold as Bakers Sugar in the USA by some companies.