Preheat oven to 170°C. Lightly grease a 4cm-deep, 27cm x 17cm (base) slice pan. Line with baking paper, allowing a 2cm overhang at both long ends.
Place butter and dark chocolate in a heatproof, microwave-safe bowl. Microwave on medium-high (75%) for 2 to 3 minutes, stirring every minute with a metal spoon, or until smooth and melted. Set aside for 5 minutes to cool slightly.
Using an electric mixer, beat eggs and sugar until light and fluffy. Add chocolate mixture. Beat to combine. Fold in flours.
Pour half the mixture into prepared pan. Sprinkle with raspberries and white chocolate bits. Pour over remaining mixture. Bake for 35 minutes or until just firm to touch (see note). Allow to cool completely in pan. Refrigerate for 4 hours or until firm.
Lift brownie from pan. Cut into squares. Dust with icing sugar. Pack into boxes.