1 large very ripe banana (approximately125g/4½oz peeled weight), mashed with a fork
250g/9oz sweet potato, finely grated
1 tsp bicarbonate of soda
50²µ/1¾´Ç³ú cocoa powder, sifted
oil, for greasing
200g/7oz self-raising flour
100²µ/3½´Ç³ú butter, cubed
3 large free-range eggs, beaten
100ml/3½fl oz semi-skimmed milk