Also known as "caster sugar" or "berry sugar", superfine sugar is the same as regular granulated sugar but ground to an extremely fine grind. With a texture somewhere between standard white sugar and icing sugar, superfine sugar is not quite a powder and is more like a very smooth sand. Because of its very fine and tiny sugar crystals, superfine sugar melts and dissolves more quickly than regular sugar, and for this reason is a great choice when incorporating sugar into a cool or lukewarm mixture, or a recipe in which the finished product is meant to be as smooth as possible.
Since the grind in superfine sugar is so fine, it dissolves quickly and smoothly into cold liquids and is a great beverage sweetener. Bartenders, for example, will often use superfine sugar as opposed to granulated sugar when making syrups and cocktails.
Superfine sugar is great for sprinkling over foods like fruit, cereal, and pastries. Because it melts and incorporates quickly, superfine sugar is often listed as an ingredient for creams, meringues, puddings, soufflés, and sorbets. If a recipe specifically calls for superfine sugar, it's generally for a reason. Using regular sugar instead will result in the same level of sweetness, but the texture of your end result will likely be grainier and less smooth.
If you're like most people and you don't have superfine sugar lying around, the good news is you can make it yourself by finely grinding regular sugar using a kitchen appliance you already own.
Start with slightly more regular sugar than the recipe calls for. Some of the granulated sugar will turn to dust as it's being ground, so you'll want to account for that when you're measuring out how much to make.
Cover up your grinding appliance with a towel to protect from making a sugary-mess of your counter.
Turn your appliance to its highest setting for 1 to 2 minutes until the sugar is very fine, almost like a powder or extremely fine sand.
Before lifting the lid, allow the sugar dust to resettle into the superfine sugar for 20 seconds. Remove your freshly-ground sugar and get baking!