For three batons:
100g sourdough starter
200g spelt flour
200g strong white flour
275g tepid water
8g table salt
Mix together your flours, water, and then the active sourdough starter. Mix using a spoon or your hands until you have a messy dough. Let this dough autolyse (rest) for an hour.
Add the salt and then knead the dough for 10 minutes by hand, or 5 in a mixter. The dough needs to become smooth and not sticky.
Leave it for 4–5 hours to bulk ferment. Perform 3-4 stretch and folds during this time to increase the dough strength.
Once bulk ferment has finished, pre-shape into three rough oblong shapes, and allow to rest for 30 minutes.
To final shape, gently roll the dough backwards and forwards until you have a baton shape. Store in a floured tea towel for 12 hours in the fridge.
Bake on a stone or steel surface for 30 minutes at 240c.