Step 1

Preheat oven to 180C/160C fan forced. Grease a 20cm (base measurement) square pan and line with baking paper.

Step 2

Use electric beaters to beat the butter, sugar and vanilla in a bowl until pale and creamy. Add the eggs, 1 at a time, beating well after each addition. Gradually sift in the flour, cocoa powder and baking powder, alternating with the sour cream, folding until well combined. Fold in the chocolate and salt. Pour into prepared pan. Bake for 30 minutes or until a skewer inserted in the centre comes out with a few crumbs clinging. Set aside to cool completely in the pan.