Heat the oven to 190C/170C fan/gas 5 and line two baking sheets with baking parchment.

Heat the butter in a small pan on the hob, or in a heatproof bowl in a microwave on high in 30-second bursts, until melted. Tip the butter into a mixing bowl if melted on the hob.

Stir the sugar into the melted butter with a wooden spoon, then beat in the egg until smooth. Stir in the mashed banana. Sift the flour, bicarbonate of soda, cinnamon and a pinch of salt into the bowl and mix until it forms a soft dough. Add the raisins, chocolate chips or nuts, if using, and stir well until evenly distributed.

Use a teaspoon to drop small scoops of the mixture onto the prepared trays, spacing them well apart as they'll spread. It should make about 24 cookies. Bake for 10-12 mins until they are light brown on the edges and feel dry to the touch.

Leave on the tray for a couple of minutes to set, then lift onto a cooling rack to cool completely. Will keep in an airtight container for up to three days.