Pour 325ml of tepid water into a large mixing bowl and add 100g of the starter, which should float.
Use your fingers to gently stir it into the water until fully dissolved, then add both flours and stir until fully mixed.
Cover with a damp cloth and rest in a warm place for 1 hour.
Combine salt and 25ml of tepid water and mix until salt is dissolved then add it to the dough, scrunching them into the dough until fully combined.
Set aside, covered, in a warm place for 30 minutes.
Wet your hand slightly and give the dough four folds in the bowl, one at each ‘corner’.
This is one turn.
Repeat this process another three times at 30-minute intervals, turning the dough four times in total across 2 hours.
After the last turn, cover and leave to rise in a warm place for another 2 hours.
To shape the loaf, tip the dough onto a clean surface and gently dust the top with a handful of rice flour.
Roughly shape into a round, being careful to keep as much air in the dough as possible.
Rest, covered, for 30 minutes.
Dust a medium bowl lined with a clean, floured tea towel.
Lightly flour the dough again and flip it over, so the flour side is on the worktop.
Set the dough in front of you and gently shape into a round.
Turn the dough over, then place it in your floured basket, banneton or tea towel-lined bowl.
Cover the dough with a shower cap (or oiled cling film) and allow to rest for 1 to 2 hours, or until increased in size by a quarter and looking bubbly.
Transfer your dough, in its basket or bowl, to the fridge to rise for another 12 to 16 hours, or until bubbly and risen by another quarter.
Place a heavy lidded casserole pot on the bottom shelf of the oven, then preheat to full whack (240ºC/464ºF/gas 9).
Bring your loaf out of the fridge and scatter rice flour over the top.
Get a piece of parchment paper, about the same size as the tea towel and put in on top of the bowl and gently press it closer to the dough and invert the bowl into your hand to catch the ball of dough.
Now the dough is on the parchment paper, carefully lift the tea towel off of the dough
Score it with a sharp knife, holding it at a 40 degree angle to the surface of the dough for the best slashes
Working carefully, remove the hot pot from the oven, take off the lid
Carefully hold the ends of parchment paper and lift the dough to the dutch oven or pot.
Using oven mitts, put the hot lid on the pot immediately but be very careful please and put it in the oven.
After 5 minutes, reduce the temperature to 230ºC/446ºF/gas 8 and bake for 30 minutes.
Carefully remove the lid and bake for a final 20 minutes, or until a malted golden brown.
Remove to a wire rack to cool.