Spelt contains gluten, I believe, as my DD doesn't use it; GS is on Gluten-free, Casein-free diet.
SR flour = self-rising flour, and yes, it has leavening in it.
Thank goodness for Google!
castor sugar: very finely granulated sugar that was formerly sprinkled from a castor.
Maybe it's the same as confectioner's/powdered sugar? Probably not, it's likely closer to superfine sugar. I just noticed the word granulated
in the def.