Mix all dry ingredients together. Add water and sourdough starter. Combine all ingredients well using a fork.
Ideally, allow the batter to soak in a warm place for about 4~12 hours.
Pour the batter on a nonstick Cookie sheet. Tint the sheet so that the batter could be evenly distribute on the sheet.
Bake at 280F for 10 minutes. Score the leather-dry crackers into squares using a silicone spatula. Bake it again at the same temperature for another 20 minutes. Turn off the oven and keep the sheet in the oven to allow the remaining heat to pull out the moisture completely from the cracks.
Store the cracks in a ziploc bag or a container.
