Cut four sheets of parchment paper to fit 9 x 13-inch (22.5 x 32-cm) baking trays.

Stir dry ingredients together. Add oil and stir to combine. Add boiling water and mix thoroughly. The dough will be quite runny at first, thickening as the corn flour absorbs the water.

Spoon one third of the dough onto each of three pieces of parchment paper. (It’s easier to spread the dough on the paper before moving it to the baking tray.)

Using the fourth piece of parchment as a cover, spread dough as evenly as you can with your hands or a rolling pin. Don’t worry if there are small gaps in the dough.

Bake at 300F (150C) for 1 hour. Remove from oven and cool on baking racks. When at room temperature, break the crackers into large pieces. Will keep for several days in an airtight container.