Cream 200g of butter and sugar together until light and fluffy.
Mix in the flour and 50mg of cocoa powder to form a soft dough then shape into a thin log on a lightly floured surface, wrap in cling wrap and refrigerate for 30 minutes.
Once chilled, cut the dough into 1/2cm thick discs and place on a lined baking tray, leaving enough space for the cookies to spread.
Bake in a preheated oven at 180C for 8-10 minutes or until the cookies are cooked through but still soft. Allow to cool.
Make the icing by beating 125g of butter until light and fluffy. Beat in 1 cup of icing sugar and 2T milk.
Sandwich the cookies together with the frosting. And serve with chocolate milk.
To make the chocolate milk, combine 40ml of sugar and 1 tbsp hot water with 30ml of cocoa powder to form a paste. Place the chocolate syrup into a glass and top up with cold milk and add a pinch of salt.