1.Preheat the oven to moderate, 180°C (160°C fan-forced). Grease a deep 19cm-square cake pan, line base and two opposite sides with baking paper.
2.Melt butter and dark chocolate in a medium heatproof bowl over a saucepan of simmering water.
3.Stir in the sugar and vanilla, then the eggs, sifted flours, white chocolate and raspberries.
4.Spread the mixture into prepared pan; bake in a moderate oven for about 35 minutes or until just firm. Cool in pan.
5.Turn out; cut into squares.