Adapted from Nigella Lawson's Nigellissima, as I loved her ingenious Italian addition of coffee powder to banana bread. However, I've reduced the sugar by well over half the original recipe's quantity, adding chestnut flour to add that rustic Corsican touch! If you can't find chestnut flour, use buckwheat for a delicious alternative.
For a gluten-free banana bread, then omit the plain flour and use 170g chestnut flour. To make muffins, pour the mixture into a greased 1x12 muffin tin (or silicone brochette moulds, so no greasing necessary) and bake for 20 minutes at 200°C (gas mark 6).
Leave the cake or muffins overnight as they'll taste even better in the morning. Store in an airtight container for up to 5 days. The muffins/cake also freeze well for up to 3 months; just defrost the night before.