Method:

1. Preheat the oven to 170ºC. Grease and dust a 15cm x 25cm baking dish.

2. Melt the butter and sugar in a pan over a medium heat.

3. Stir in the flour and vanilla, and crack in the eggs, then divide between 2 bowls.

4. Chop the dark and white chocolate, keeping them separate. Chop the nuts.

5. Mix the cocoa, dark chocolate and half the nuts into one bowl, then stir the white chocolate and remaining nuts into the other.

6. Place alternate spoonful into the prepared dish, swirling it through.

7. Bake for 30 to 40 minutes, or until an inserted skewer comes out clean.