Well, I have sent the recipe to some of you, but now it makes sense to pop it up here instead!
375g butter or marge
190g icing sugar (confectioner sugar)
375g plain flour
125g custard powder
Cream butter and icing sugar together (I use my mixer, which is my ancient Kenwood)
Add the flour/custard powder mixed together spoon by spoon as the mixer whirs about on a low speed.
Roll walnut sized balls of cookie dough in hands and pop on baking sheet. Press down with fork dipped in flour so it doesn't stick. Bake at 180C (350F) for about 12 minutes. Or until the base looks golden. Allow to cool and then either eat plain, or you can sandwich them together with melted chocolate, or dip them into chocolate, like I did, or you can sandwich them together with butter icing. Any way, they are delicious and family favourites around here.
Custard powder is essentially cornflour (cornstarch in the US - here is Vee's research link explaining custard powder! - Thanks, Vee!) mixed with powdered egg and a little sugar I think. I have used plain cornflour and a teaspoon of vanilla essence instead when I have run out and they tasted great. I imagine almond essence would also be good. Hmmm. I must try that one.
I hope they work for you and that you enjoy them!
Edited to add December 2012 : I gather the last link doesn't work any more. Just add vanilla pudding mix. Here is a link about using alternatives. Enjoy!