Preheat oven to 160 degrees. Place chocolate bar pieces and butter in a saucepan over low heat and stir until smooth. Allow to cool slightly.
Place sugar, eggs, cocoa, flour and baking powder in a bowl. Add the melted chocolate mixture, whole chocolate pieces, macadamias and combine. Do not overwork the mixture as it can make the brownies tough.
Pour mixture into a 20cm (8 in) square slice tin lined with non stick baking paper cut in two pieces.
Bake for 50 minutes or until set. If checking with a skewer, the chocolate melted through will be gooey, but the slice is cooked.
Cut into slices in tin.
Serve warm with double cream or great cold! Enjoy!