Preheat the oven to 180 C, 350 F, Gas Mark 4
Grease a baking tray.
Add the flour and salt to a bowl with the butter or margarine.
Rub the butter into the flour until it resembles fine breadcrumbs.
Cut the chocolate into small chunks using a knife or scissors.
Add the chocolate and sugar to the flour and mix. Make a well in the centre of the mixture.
Add the milk, egg and vanilla essence and mix until it forms a stiff dough.
Using two forks make 12 heaps of the mixture on the baking tray.
Bake for 10-15 minutes until lightly brown.
Leave to cool on a wire rack.