Mix all the dry ingredients in a bowl and pour over the boiling water, stir well.
Leave for 20 minutes, this is non-negotiable! The seeds absorb the water and the mixture becomes a firm gel.
Roll out thinly between two sheets of baking parchment.
Bake at 150°C for 30–45 minutes (sometimes longer, every oven is different). They should feel firm when they come out and they crisp up a little more as they cool.
Store in an airtight container for up to 5 days.
