Mix active starter with rye flour and starter. Place it somewhere warm and let it ferment until it has at least doubled in volume

Mix flour with water until all flour is hydrated. Let the dough rest for 1 hour.

Add salt and levain and knead the dough for 5 minutes. Let the dough rest for 15 minutes.

Perform a set of stretch and fold, followed by two more, spaced out by 30 minutes.

Let the dough ferment until it has increased by 50% in volume.

Dump out the dough on a floured surface and shape it into a round. Let it relax for 15 minutes and shape it into a batard or other preferred shape.

Place the dough into a floured banneton and let it proof for about 1 hour at room temperature, and 8 hours in a refrigerator.

Preheat the oven to 250°C, and bake for 45 minutes.