Step 1

Preheat oven to 160°C. Brush a 16 x 26cm (base measurement) slab pan with melted butter. Line with non-stick baking paper, allowing the sides to overhang.

Step 2

Place chocolate and butter in a heatproof bowl over a saucepan half-filled with simmering water (make sure the bowl doesn't touch the water). Use a metal spoon to stir until the chocolate melts and the mixture is smooth. Set aside for 5 minutes to cool slightly. Add 2 eggs and whisk to combine.

Step 3

Combine the flour and 100g (1/2 cup) caster sugar in a large bowl. Sift in the cocoa powder. Stir in the chocolate mixture until just combined.

Step 4

Use an electric beater to beat the cream cheese, sour cream and remaining sugar in a bowl until smooth. Add the remaining egg and beat until just combined.

Step 5

Spoon the chocolate and cream cheese mixtures alternately into the prepared pan. Use a skewer to create a swirled effect. Bake for 50 minutes or until crumbs cling to a skewer inserted into the centre. Set aside in the pan for 3 hours to cool.