Thanks Shan! I just got this recipe from Em which is ever so slightly different!

185g butter
60gt icing sugar
60g custard powder
185 g plain flour

Cream the butter and icing sugar. Sift the custard powder and flour 3 times and then add to the butter/sugar mixture and combine. Roll into walnut-sized balls and flatten with a fork on the tray. Oven 160 C for 15 - 18 minutes. It took a bit over this in my oven which seems to be a bit on the slow side!

I also put the following filling in it:

1 cup icing sugar
1 1/2 tbsp cocoa
1 tbsp boiling water
1/2 tbsp vanilla essence

Beat the icing sugar, cocoa, water and butter and add vanilla essence.

YUMMO!!! These are so delicious!