Preheat the oven 160℃ (fan). Line a baking tray with parchment paper. Mine measures 40 x 30 cm.
Place all but 20g of the seeds in a bowl with the cornflour, add the oil and fine sea salt. Stir to blend the ingredients. Just as the kettle finishes boiling, carefully pour the water over the seed mix and give it a good stir.
Pour the mixture immediately onto the tray and spread evenly with an off set spatular, making sure there are no gaps. Sprinkle the remaining seeds on the top, and then add a light sprinkling of Maldon sea salt flakes. Place in the oven and bake for 15 minutes.
Remove the tray from the oven to cut into squares or rectangles. Now return the tray to the oven to crisp up. Continue to bake for one hour, then turn the oven off.
Once cool, store in an airtight container for up to 2 weeks.
Notes
To ensure the crispbread is completely crisp, once they're done, turn the oven off and leave the door open for 5 minutes to cool down quickly. Then shut it and leave the crispbread there for several hours.