Sift flour and custard powder (or cornflour) together and slowly mix into the butter and sugar until all combined. If the mix is too soft to roll into balls pop the bowl in the fridge to set for 10-15 mins. Roll into balls, place on a liked tray and flatten with a fork dipped in water.
Bake in a preheated 175*C oven on a lined tray for about 10-15mins. Cool and freeze if you wish.
To me this made a cakey biscuit (it rose too much) and I'm not a fan of those, I think next time I might try substituting some plain white or wholemeal flour (1 cup at a time to find the right combination) instead of all self raising flour.
My next tray when it went in I set the timer to the 8 minute mark, I grabbed my fork again, just pressed down a little on those rising biscuits and popped in again for about 2-3 more mins. This gave me a more crisp biscuit and I baked all the rest of my biscuits this way, perfect for us.
The pictured biscuits are ones I mixed some with milo (like quik/ovaltine) then sprinkled milo on top to bake. The others I mixed in some ginger and spices sprinkling raw sugar on top. There were also some of the usual choc chips but they were eaten before I had a chance to photograph.
The options on flavours are plenty, divide, make and bake the whole batch and have a wonderful variety to pick out of the freezer when needed.