- 200g/7oz self-raising flour
- 50g/1¾oz cocoa powder
- 1 tsp bicarbonate of soda
- 100g/3½oz butter
- 100ml/3½fl oz semi-skimmed milk
- 3 large free-range eggs
- 250g/9oz sweet potato, finely grated
- 1 large very ripe banana, mashed
- Preheat oven to180C. Grease and line a 9in loose-based square cake tin with baking parchment.
- Mix flour, cocoa and bicarbonate of soda in a large bowl.
- Melt the butter in a saucepan over a low heat. Take pan off the heat and stir the milk into the melted butter. Add the eggs, sweet potato and banana, stirring vigorously.
- Add wet mix into the flour mixture. Stir to bring batter together. Pour into the prepared tin.
- Bake in the centre of the oven for 30-35 minutes.