Method

1. Preheat the oven to 170C/150C Fan/Gas 3 and line two baking trays with baking paper.

2. Briefly whizz the oats in a food processor until they are chopped to half their original size. Add the bicarbonate of soda and whizz for another 5 seconds then tip into a mixing bowl.

3. Add the peanut butter, sugar and egg (and raisins if using) and mix until thoroughly combined.

4. Roll the mixture into walnut-sized balls and arrange on the trays, leaving a little space between each one. Flatten each cookie to about 1cm/½in thick.

5. Bake for 12–14 minutes until crisp and starting to turn golden brown. Leave the cookies to cool on the baking tray to firm up.