I know I should know this. Maybe I do, and pg brain is suppressing it somewhere?

Why in some recipes, like the one I've put below, do they ask for all the different types of flour? Ie, plain flour, rice flour, and cornflour.

And is there any difference (in the end result) in using caster sugar instead of icing sugar in a situation like this recipe? I made something the other day (similar slice and bake biscuits) just with caster sugar, because I didn't have any icing sugar, and I think the icing one is too expensive to want to use two cups worth (it was nearly that much in the other recipe) to use in dough. Rather use it as icing, iykwim. The biscuits I made, I hadn't made before, so I can't compare them to how they *should* be.

Slice and Bake Cookies (from AWW "cookies" book)

250g butter, softened
1 ? cups icing sugar
1 tsp vanilla extract
2 cups plain flour
? cup rice flour
? cup cornflour
2 tblsp milk

Beat butter, sifted icing sugar, and vanilla in small bowl with electric mixer until light and fluffy. Transfer to large bowl; stir in sifted flours, in two batches, then add milk.

Divide the mixture in half. Knead each half on floured surface until smooth, then roll each half into 25cm logs. Wrap each log in baking paper; refrigerate about 1 hour or until firm.

Preheat oven to 160?C/140?C fan-forced. Grease oven trays; line with baking paper.

Cut logs into 1cm slices; place about 3cm apart on oven trays. Bake about 20 minutes. Cool on wire racks.


Sorry, another question about flour! I have a yummy recipe for buttermilk and sultana muffins, which asks for plain flour with baking powder. That's cool, I get the powder is to raise the muffins. But, can I just use self raising flour? I was talking to my Mum about this last week, and she made choccie muffins too, that she said were not good at all, and she thinks it is because she used SR flour, not plain + powder. I think they rose, they just made her feel ill.
Again, its a cost thing , and I'm interested to know where I can substitute things. For the size batches of muffins I'm making atm, I use probably about a third of a container of baking powder in one go!

Any ideas? Thank you all you clearer thinking geniuses!