Make the dough: Add the sourdough starter and melted butter to a mixing bowl and stir well. Add the plain flour, herbs and chilli flakes. Mix until a soft dough forms.
Rest: Cover the dough and leave it to rest for 20–30 minutes. If the dough feels very sticky, add a little extra flour, one tablespoon at a time.
Preheat the oven: Heat the oven to 180°C / 350°F and line a baking tray with baking paper.
Roll the dough: Divide the dough into two portions. Place one portion between two sheets of baking paper and roll very thinly, ideally around 1–2 mm thick.
Season and cut: Remove the top sheet of baking paper. Sprinkle the dough with sea salt and, if desired, a little extra herbs or chilli flakes. Score into squares or rectangles using a pizza cutter or sharp knife.
Bake: Transfer the baking paper and rolled dough onto the baking tray. Bake for 15–22 minutes, or until the crackers are dry, crisp and lightly golden. Check frequently towards the end as the edges may brown faster.
Cool: Allow the crackers to cool completely. They will become crispier as they cool. Break along the scored lines and repeat with the remaining dough.
Store: Once completely cool, store in an airtight container at room temperature for up to 5–7 days.
Notes
Roll them thinThis is the secret to really crisp crackers. Thick dough will give you something closer to a savoury biscuit, while very thin dough produces delicate, crunchy crackers.Keep the thickness evenUneven dough means some crackers may burn while others remain soft. Take a little extra time during rolling to achieve a reasonably even sheet.Watch the final few minutes carefullyCrackers can change from beautifully golden to over-browned quite quickly, particularly around the edges.