Place the flour, cocoa powder and brown sugar in a bowl and mix together. Cut the butter into small pieces and rub into the dry ingredients with your finger tips. This will turn into a soft dough, but try to remove the large pieces of butter.

Finely chop the chocolate and mix into the dough with the condensed milk. Once combined, roll the dough into two logs and place in the fridge to chill for 30 minutes. Preheat the oven to 180ºC.

When the logs are chilled, cut them into 1cm rounds and place on baking trays, with eat least 1cm surrounding them. Bake for 12-15 minutes. Once cooked leave until solid and then cool completely on a cooling rack.