Cut 1 cup of the butter into the flour until the mixture resembles coarse crumbs. Stir in the cream and form the dough into a ball.
Roll dough out 1cm thick and cut with a small round cutter. Roll cut circles in white sugar and place on ungreased baking sheets. Prick biscuits a few times with a fork.
Bake for 8 to 10 minutes. Let biscuits cool before icing.
To assemble: ice bottoms of half of the biscuits and place the remaining biscuits on top to make sandwich biscuits.
To make buttercream icing: Beat 1/2 cup of the butter until fluffy. Gradually add the icing sugar. Beat in the evaporated milk and the vanilla. Adjust milk and icing sugar amounts to get buttercream to a good spreading consistency.