Preheat the oven to 180°C, fan 160°C, gas 4. Whiz the porridge oats in a food processor or blender to make a coarse flour. Tip into a large mixing bowl and stir in the plain flour and cayenne pepper.
With your fingertips, rub the butter into the oat mixture until it resembles fine crumbs. Use 3 tbsp cold water to create a dough, then lightly knead until smooth.
On a lightly floured surface, roll out to a thickness of about 4mm. Using a small Christmas tree cutter, stamp out 16 biscuits (you’ll need to re-roll the dough).
Place on a lined baking tray and lightly brush all over with the egg white. Scatter over the seeds and bake for 30 mins until dry and crisp. Leave to cool on the tray for 5 mins, then transfer to a wire rack to cool completely. Store in an airtight container for 3-5 days.
Cook’s tip: for gift ideas, pile biscuits in a box lined with tissue paper and give with a jar of chutney. These cheesy crackers go hand in hand with homemade chutney.