Just found the recipe similar to Lisa's that I have used: (and it makes about 120 biscuits!)

500g margarine or butter
1 tin condensed milk
1 cup sugar (I use slightly less, maybe 3/4)
5 cups self raising flour

Cream butter and sugar, add condensed milk and flour. Roll into teaspoon sized balls and press down with fork. Onto greased trays, bake in moderate oven for 10-15 mins.
Variations inc; choc chips and chopped glace cherries / cornflakes and sultanas / hundreds and thousands / milo and coconut / etc.

I also had the thought before about making red velvet sandwich cookies... (look on Bakerella for a pic, but with my usual french cream icing )