Preheat the oven to 180°C and line a 9"x9" baking pan with baking paper and set aside.
Place the brown sugar, flour, cocoa, baking soda, baking powder and salt in a bowl and mix together.
Melt the oil and dark chocolate together and mix into the dry ingredients. Add in a tablespoon of milk at a time until the mixture comes together.
Add in the chocolate chips and stir through.
Press into the prepared pan and place in the oven for 15-20 minutes. The middle will be soft and they will look slightly underdone but they will harden as they cool.