Preheat the oven to Gas 4, 180°C, fan160°C. Grease and line an18x28cm (9x11in) tin with nonstick baking paper.
Melt the chocolate and butter in a small pan over low heat, stirring until smooth. leave to cool for 10 minutes.
Whisk the eggs and sugar together in a bowl and stir in the cooled chocolate mixture and vanilla extract. Sift in the flour and baking powder, chocolate chips, soured cream and macadamia nuts and stir to combine.
Spoon mixture into the prepared tin and spread to the corners. Bake for 40 minutes then remove from the oven, cover tin with foil and bake for 20 minutes more. Remove from the oven and allow to cool before cutting into pieces.
When the brownies have cooled it's nice to dust them with sifted cocoa powder.
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