Add the starter dough mixture to the bowl and knead for 10 minutes. This is a wet dough, so using a food processor with a dough hook attachment works well: run it on a slow speed for 5 minutes, then on a fast speed for another 5 minutes.
Tip the dough out onto a generously floured surface, dust with more flour, cover, and let it rise for 30 minutes. The dough will be quite sticky, so don't be shy with the flour. At 10-minute intervals during this rise, use your hands to gently punch the dough flat, stretch it out, fold the edges over themselves, and turn it over.
Grease your loaf tin. Shake off any excess flour from the dough, form it into a loaf shape, then place it in the prepared tin. Cover and leave to rise for a further 30 minutes. After the dough has been rising in the tin for 10 minutes, use a very sharp knife to score a 2 cm line down the center of the dough; this helps create a good crust. Preheat your oven to 230 °C.