The perfect cookie! Also really easy to make.
150g caster sugar
1 egg yolk
250g self-raising flour
25g cocoa powder
100g plain dark, milk or white chocolate, broken into squares
1 Tbsp milk
Cream the butter and sugar together until pale and fluffy. Add the egg yolk, then sift in the flour and cocoa powder. You might need to add a little milk now too. Mix together until a firm dough is formed. Knead lightly on a floured surface, then wrap in cling-film and chill for 20 minutes.
Roll out one quarter of the dough and cut into 9 circles, using a 2ins cutter. Put a square of chocolate on each circle of dough. Roll out another quarter of dough, cut out another 9 circles then use these to sandwich the chocolate squares, pressing the edges well to seal. Repeat with any remaining dough.
Bake in a pre-heated oven 190C/gas mark 5, for 10 minutes. Cool for 10 minutes on the tray before transferring to a cooling rack.