how impoartant is it to use caster (superfine) sugar in a recipe if it calls for it?

Throw granulated sugar in your food processor or blender...won't need a lot of time so don't overprocess.

You can substitute regular sugar unless the reason for using the superfine sugar is for it to dissolve. If that's the case, use the same amount of regular sugar, pop it in your food processor and pulse for a few seconds, then use. I substitute regular sugar in most recipes that call for superfine and never have a problem...

If it calls for superfine sugar and you can find it you should use that. It depends on what your making. When it comes to making candy or confections, you have to use cane sugar, if you don't it will never come out right. Some store brand sugars are beet sugar and not cane. It will not set at the hard candy stage (like peanut brittle), if you use beet sugar, it stays soft.

The food processor solution is the cheapest. However, superfine sugar is also "bar sugar" and may be found in full service liquor stores.

Absolutely! Superfine sugar dissolves quicker. It's between granulated and powdered sugar. Granulated will taste sweeter. If you're baking pastries it will come out rock hard. Baking is all about chemistry.

Stick the sugar in the blender or a food processor. Make your own castor that way.

You can whirl the requested amount of sugar in a blender for a minute or so. I think the purpose for this ingredient in a recipe it that plain sugar may feel grainy in the eating of it.

You can always try it. But try putting regular sugar in your food processor.

it depends on the recipe, and the procedures and techniques used in it.

Depending on what moment and the purpose to what sugar is required, it may be replaced or not.

The difference will be in the texture of your finished product. Course ingredients make for course texture; i.e: regular flour vs. cake flour.