Superfine sugar is simply granulated sugar ground more finely. It's called for in recipes where a faster dissolving granule is needed, such as in the meringue for this Baked Alaska. It's available at most supermarkets, but you can also make it at home. Put the amount of granulated white sugar called for in your recipe in a food processor. Add a couple of tablespoons more to compensate for a reduction in overall volume. Process for 1 to 2 minutes until the sugar feels like fine sand, letting the sugar dust settle before opening your food processor to check. Remeasure before using.