Superfine sugar is also known as bar sugar or caster sugar. It’s great for easily dissolving into cold liquids. If you only have granulated sugar on hand, you can use a blender or coffee grinder to pulse the sugar into finer crystals — but not into a powder. Do NOT substitute with confectioners’ sugar. Alternatively, make a simple syrup by boiling equal parts water and granulated sugar in a small saucepan until the sugar is dissolved; let it cool before adding it to the rest of the mixture.