Step 1

Preheat oven to 180°C. Grease a 20cm (base measurement) square cake pan and line the base and sides with baking paper, allowing the sides to overhang. Combine the butter and chocolate in a medium saucepan over low heat. Cook, stirring, for 5 mins or until the mixture is smooth. Set aside for 5 mins to cool slightly.

Step 2

Add the sugar and stir to combine. Stir in the eggs until well combined. Add the flour, cocoa powder and sour cream and stir to combine.

Step 3

Spoon the batter into the prepared pan and smooth the surface.

Step 4

Bake for 30-35 mins or until a skewer inserted in the centre comes out clean. Set aside in the pan to cool slightly. Cut into pieces to serve.