Combine all dry ingredients and gently stir with a whisk. Using a whisk means there is no need to sift the flours.
Add the starter to the water and thoroughly mix together.
Pour the liquid into the flour and mix with a wooden spoon. Combine all ingredients properly. At this stage the dough will look quite sticky and shaggy, this is exactly what you want.
Cover your mixing bowl with cling film and leave the dough to rise for 12-18 hours. The bowl should be out of direct sunlight as you don’t want the dough to rise too quickly. The slower the rise, the more time the flavour has to develop. You will know when the dough is ready after it appears that the dough has stopped rising. For me, this was 12 hours, but it was a warm day and our kitchen is the warmest room in our house.
Generously flour your countertop, and flour the dough in the bowl. This should prevent the dough from sticking to the side of the bowl as you scrape it out on to the counter.
The dough will be quite loose at this point and you will be able to see it slowly spread across the counter.
Add some more flour to the top of the dough then gently spread it out with your fingertips to flatten it out, and pop any large pockets of air. You might need to apply even more flour to the top if the dough is sticking to your fingers.
Once you have a rough square shape, grab the far left corners of the dough, then give the dough a little stretch and fold from left to right so two-thirds of the dough is folded.
Grab the two far-right corners and give the dough another stretch and fold so the remaining third is laying on top of the first folds.
Then grab the bottom two corners, give a little stretch towards you, then fold into a third away from you.
Grab the last two corners at the top, give a little stretch away from you and fold the dough towards you.
With the aid of a board scraper, turn the dough over and apply some flour to the top of the dough.
Cup both hands under the dough and rotate your hands. I do it anti-clockwise, but feel free to do it clockwise if it feels better. The point here is to build some tension into the dough so it holds its shape. Do this a few times until you have a round boule shape.
Flour the boule, cover with cling film and leave to rest for 20 -30 minutes.
Generously flour a round banneton to prevent the dough from sticking during the second rise.
Repeat the cupping motion to apply more tension to the surface of the dough. Apply more flour when needed to prevent sticking. With each turn you will see the surface of the dough pull tighter, the aim of this is to make the surface tension tight enough to hold the shape of the bread when cooking, and not make it so tight that the surface of the bread rips, so please don’t over tighten.
Flour the top of the bread, and place upside down into the floured banneton.
Cover so it doesn’t dry out (a shower cap works greats for this) and leave in the fridge overnight to rise again.
Place a cast iron pot (with a lid) in an oven and preheat to 250 C for 30 minutes.
While the oven is preheating take the dough out of the fridge to remove the chill.
After 30 minutes turn the dough onto a piece of baking paper. This makes it much easier to place the dough into the cast iron pot.
Score the top of the dough to allow the bread to expand in a controlled manner.
Carefully place the dough on the baking paper into the cast iron pot, cover with the lid and place it into the oven. Bask the bread for 20 minutes at 200 C. Be very careful when taking the pot out of the oven and don’t forget to use gloves when putting the lid back on as it's very hot.
After 20 minutes remove the lid and bake for a further 25 minutes.
To check that the bread is thoroughly cooked, the loaf should have a hollow sound when you tap the bottom. It should also have an internal temperature of 93 C if you have an instant-read thermometer handy.
Please wait for the bread to cool before cutting. If you cut the bread while it's still hot, the released steam will cause the bread to get a little bit soggy.