Description
You can find this stuff at the grocery store. It goes by a variety of names, such as baker’s sugar, bar sugar, superfine sugar, berry sugar, and, in Britain, castor sugar. I usually refer to it as bar sugar.
C&H Baker's Sugar works great. You don't want to use powdered or confectioner's sugar--this stuff has corn starch in it to prevent clumping. That would not do too well in a drink.
Domino Superfine Sugar also works great.
Finally, C&H Superfine Sugar does very nicely. This one can be a bit harder to find.
Keep your bar sugar in a tightly sealed container, as it is prone to clumping. I keep mine in a glass canning jar.