1. Mix 400g strong white flour (13-14% protein) with 100g dark rye flour and 325g filtered or bottled water. Make sure no lumps, cover and leave to autolyse for 6 hours.
2. Mix autolysed mixture with 10g salt and 100g active sourdough starter and leave to rest for 15 minutes.
3. Stretch and fold 4 times leaving 40 minute gaps rest.
4. Leave to rest until risen 25%.
5. Preshape and leave to rest for 15 minutes on a floured worktop.
6. Final shape into boule or batard and gently rub with rice flour.
7. Place in banneton, seal within carrier bag and leave to rise for 1 hour at room temperature.
8. Retard in fridge at 4C overnight and preheat oven at 250C for 1 hour.
9. Remove from fridge, rub with rice flour, score, slide into oven on wooden peel.
10. Bake either on pizza stone with lava rocks with boiling water poured on for 15 minutes at 250C and then 25 minutes at 210C OR 20 minutes inside a dutch oven at 250C plus 20 minutes at 210C uncovered.