Mix the Levain ingredients together in a small bowl until completely combined. Cover it and leave it at room temperature overnight.
Day 2: Making the Dough
The following morning start the dough. Combine the different flours, the levain and the water and mix till it forms a shaggy ball and the flour is all hydrated. Cover it and leave it to rest for an hour.
Add the salt and the extra 10g of water and mix to combine. Cover the dough and leave to rest for half an hour.
Stretch and fold the dough 4 times at half hour intervals (this will take 2 hours). At this point the dough should feel smoother. After you’ve finished the stretches recover the dough and leave it for 2 hours.
Tip the dough onto a lightly floured surface and gently shape it into a ball by stretching the sides of the dough up and into the middle and then flipping the whole thing. You should get a ball thats smooth on top. Leave on the counter uncovered for 10 minutes while you prep your proofing basket. You can either use an oblong proofing basket or a loaf pan lined with a kitchen cloth and dusted with flour.
Back to the dough! Shape it into a batard. This can feel tricky at first but just take it slowly and it’ll be fine! Start by flipping the dough over on the counter. Stretch the left side up and over into the center and then repeat with the right hand side. Next fold the top down half way. The next step is to fold the bottom up 2/3rds of the way and pinch to seal. Finally you’ll pinch along the seam at the bottom to seal your loaf. Look at the pictures above if you’re feeling lost!
Now lift your dough and place it seam side up in the proofing basket. Place it in a plastic bag or cover with clingfilm and leave it on the counter for 20 minutes before placing it in the refrigerator over night.
Day 3
Place a dutch oven in your oven and preheat to 500°F for 45 minutes.
When your oven is almost ready take the dough out of the fridge and uncover it. Carefully invert it onto a piece of parchment paper the size of your loaf.
Dust the top of the dough with flour and use a sharp knife or a lame to score the dough. You want to score it at a 45° angle and your cut should be about 1/2 an inch deep. Again look at the pictures for an idea of what this should look like.
Carefully lift the dough up using the parchment paper and drop the whole thing into your dutch oven. Cover with the lid, turn the oven down to 475°F and bake for 25 minutes.
Uncover the bread and continue baking for another 10-15 minutes until it is properly browned. If you have a thermometer check that the internal temperature reaches 207° F. Leave the loaf to cool for 2 hours before slicing!