Add flour, sourdough starter, and water to the bowl of a stand mixer. Mix on low speed for 5 minutes until the dough is smooth and fully combined. Transfer to a clean bowl, cover with a damp towel, and let rest for 30-45 minutes.

Sprinkle 10g salt over the dough. Add a small dash of water to dissolve the salt, then mix by hand until fully incorporated.

Use the stretch and fold technique to strengthen the dough. Stretch one side upwards, fold it over, rotate the bowl, and repeat 3-4 more times. Let rest for 30 minutes, then repeat for 3-4 rounds.

Cover the bowl and let the dough rise at room temperature for 4-6 hours or until doubled in size.

Lightly flour your surface, shape the dough into a round or oval, and place it seam-side up in a proofing basket or bowl lined with a towel.

Cover and place the dough in the fridge for 12-24 hours for cold fermentation.

Preheat the oven with a cast iron Dutch oven (with the lid on) at 250°C (482°F) for 30 minutes.

Remove the dough from the fridge, score deeply once with a sharp knife, and transfer it to the preheated Dutch oven. Bake covered for 5 minutes.

After 5 minutes, remove the lid, make a shallow score to help the loaf expand, and bake for another 15 minutes.

Lower the temperature to 220°C (428°F) and bake uncovered for another 10 minutes until golden brown. Remove from the oven and let cool for at least 1 hour before slicing.