Can you use superfine sugar instead of regular in baking?

Yes because superfine sugar is regular granulated sugar it's just been ground into finer crystals so it can be dissolved easier in many light recipes where you would not want the grainy texture of regular sugar, like in merinques and angel food cake. You can use superfine sugar in any recipe and be successful, it's when you try to substitute regular granulated sugar when it calls for superfine that you run into trouble because it will be too grainy or possibly lumpy. You could always make your own version of superfine sugar by putting regular granulated sugar into a food processor and chopping it up for a minute or two and it would be simliar to store bought superfine sugar.