All purpose flour vs plain flour

[Rojak]

Please help this novice baker.

I want to make some shortbread with the DCs and I've bought some plain flour, only to check my recipe and it says "all purpose flour".

Does it matter if I use plain instead of all purpose?

While I was at baking shop, I also noticed something called superfine flour - what is that?

Thanks

I think it's the same. All purpose doesn't have any raising agent.

All-purpose flour is the US term for what's known in the UK as plain flour.

Superfine flour is milled extra fine - it's meant to make it easier to make sauces etc without lumps.

Great, thanks for the very quick response.

On a similar note, how much baking powder would you add to flour to make it "self-raising"?

1 and 1/2 tsp baking powder per cup - can't remember what it is in weight but most cookbooks have it at the front.

Thanks