Step 1

Preheat oven to 160°C. Grease a deep 20cm (base measurement) springform cake pan and line the base with baking paper. Use an electric mixer to beat the butter, sugar and vanilla in a large bowl until pale and creamy. Beat in the chocolate. Add eggs, 1 at a time, beating well after each addition.

Step 2

Sift flour and cocoa powder into a medium bowl. Add flour mixture and 1/2 cup (125ml) custard, in alternating batches, to the butter mixture and fold to combine. Spoon one-third of the cake batter into the prepared pan. Use a flat-bladed knife to make indents in surface.

Step 3

Combine remaining 3/4 cup custard with cornflour in a bowl. Spoon half the custard mixture over the indents. Continue layering with remaining cake batter and custard mixture, finishing with cake batter. Bake for 1 1/4 hours or until a skewer inserted in centre comes out clean. Set aside in the pan to cool slightly.

Step 4

Transfer the cake to a platter. Dust with icing sugar. Serve warm with raspberries and extra custard.