1) First, prepare the leaven. Put room temperature sourdough starter into a bowl, add rye flour and lukewarm water and mix together until you get a ‘thick batter’. Cover and leave to rest in a warm place for five to eight hours. 

2) Put the spelt flour into a stand mixer’ bowl, add the crushed cumin seeds and salt and mix together. Add the leaven, buttermilk, lukewarm water and using a dough hook, start kneading gently on speed one. Mix for five minutes, then increase the speed to two and continue kneading for another three minutes. If the dough looks thinner than you’d like, add a little bit more flour and knead it in. 

3) Place the dough into a well greased bowl, cover it with a cling film and let it rest for about 45 minutes. Meanwhile, dust a banneton basket with some rye flour or cornstarch. 

4) Once the dough has rested, stretch and fold it four times, cover it again with a cling film and let it rest for further 30-45 minutes. Once rested, repeat the stretch and fold again and rest the dough yet again for 30-45 minutes. 

5) Tip the dough out onto a floured surface. Stretch and fold the dough several times, making sure you remove any air bubbles at the end. Shape and place the dough into the banneton basket, cover it and let it rise for about five hours in a warm place. 

6) Heat the oven to 250C/230 fan. Prepare one baking sheet and a heatproof bowl filled with about 200ml of water. Tip the bread out onto a parchment (baking) paper and using a sharp knife or a razor blade, make a shallow cut in the center of the dough. Place both the baking sheet and the bowl with water in the preheated oven, with the bowl placed at the bottom of the oven. Leave the bread on the parchment, spray it with a bit of water and place it on the hot baking sheet.

7) After 20 minutes of baking, remove the bowl with water. Please, apply extra caution when opening the oven as there will be quite a bit of build up of hot steam.

8) Leave the oven door very slightly ajar, prop it with a wooden spoon; to remove any remaining steam. Lower the temperature to 190C/170C fan and bake for another 20 minutes or so. 

9) Remove bread from the oven, place on a cooling rack and let it cool down. Enjoy!