In a large bowl, using a wooden spoon or rubber spatula, mix the warm water with the sourdough starter. Stir in both the whole-wheat and bread flour and the salt until a shaggy dough forms. Using your hands, squeeze and mix the dough until evenly moistened and all the dry flour is incorporated.

Cover and let rest in a warm part of the kitchen for 4 hours; stretch and fold the dough over itself every 30 minutes to 1 hour.

After the 4 hours, keep the bowl covered and let the dough rest in a warm part of the kitchen until increased by 50%, about 8 hours or overnight. At this point, the dough should be supple and jiggly.

Very lightly dust a work surface with all-purpose flour. Gently scrape the dough onto the work surface; do not flour the dough. Working your way around the dough, gently stretch the side out and fold it over the centre, forming a rustic ball. Using a bench scraper, flip the dough so the folds are on the bottom and let rest for 15 minutes.

Meanwhile, line a 20 to 25cm bowl or proofing basket with a clean kitchen towel and dust it with white rice flour.

Using a bench scraper positioned under the side of the dough furthest from you, gently pull the dough towards you across the work surface, rotating slightly as you drag it to form a taut ball. Repeat this process 3 more times for a total of 4. Using a bench scraper, quickly and carefully invert the dough seam side up into the prepared bowl or basket. Lightly dust the top with white rice flour, cover, and rest in the refrigerator overnight.

The next morning, preheat the oven to 260°C for at least 30 minutes. Place the Le Creuset Bread Oven into the oven to heat up for 30 minutes to 1 hour before placing the dough inside. Brush the base of the Bread Oven with olive oil. Dust the boule with white rice flour. Using a razor blade or a very sharp, thin knife, score the boule decoratively (0.5-1.2cm deep) on the baking paper and then lift with a scraper into a preheated pot. Oven with the domed lid and place it in the preheated oven. Reduce the temperature to 230°C and bake for 30 minutes until the boule is risen. Remove the lid and continue to bake the boule for 20-30 minutes more, until golden brown. Immediately transfer the boule to a rack and let it cool completely before slicing.