1 cup mashed banana (you will need 2 large, very ripe bananas)
2 1/4 cups self-raising flour
1/4 teaspoon bicarbonate of soda
180g white chocolate, chopped
1/4 cup sour cream
Step 1Preheat oven to 180°C. Grease base and sides of a 7cm deep, 19cm square cake pan and line with baking paper.
Step 2Using an electric mixer, beat butter, sugar and vanilla until pale and creamy. Add eggs, 1 at a time, beating well after each. Using a metal spoon, gently fold in sour cream and bananas. Sift flour and bicarbonate of soda over batter and gently fold through.
Step 3Spoon batter into cake pan. Smooth surface. Bake for 50 to 60 minutes or until a skewer inserted into the centre comes out clean. Stand for 5 minutes before turning out onto a wire rack.
Step 4Make icing Place chocolate and sour cream in a heatproof bowl over a saucepan of simmering water. Heat, stirring constantly with a metal spoon, for 3 minutes or until smooth. Remove from heat. Stand for 10 minutes or until slightly thickened. Pour icing over cake, allowing it to drizzle down sides. Serve warm.