Place half the chocolate and butter in a small saucepan over low heat and stir until melted and smooth. Allow to cool slightly.
Place the sugar, eggs and flour in a bowl with the chocolate mixture and mix to combine.
Stir through the remaining chocolate pieces and pour the mixture into a lightly greased 20 cm x 30 cm tin lined with non-stick baking paper. Bake for 30-35 minutes or until cooked when tested with a skewer. Allow to cool in tin and cut into squares.