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Mix the starter ingredients together. It doesn't matter that much how much previous starter you use - just take off exactly the same amount of mixed up starter as you added previous starter, so that you end up with 410g of starter. I tend to add the whole of my previous starter, and take away the same amount, so that I always referesh my starter completely. This keeps it nice and bubbly, and prevents it from going off.
Let the starter sit for 5 to 12 hours until it's nice and bubbly. You will still be able to see the individual oats, which we don't want for our bread. So take a spoon and mix the starter nicely until it turns into a smooth paste, with no more individual oats visible.
Now add all the ingredients for the main dough to the starter, and let it autolyse for half an hour. Then stretch and fold 4 times, and let it sit for another half an hour. Repeat until you can feel a good amount of air bubbles in the dough, and you have the right consistency - stretchy, bubbly, light. This will take up to 4 hours depending on room tempearture.
Form and flour the dough and put it in your proving basket or your bread tin for the final proof - depending on your room temperature, 1 to 2 hours. You want a further increase in volume of about a quarter.
Don't overprove on the second proof as you won't get a proper rise during baking.
Now preheat your oven to 230 degrees, turn out the dough from the proving basket (or keep in your tin), and score the top. Put into the oven, to which you have added a cup of water onto a baking tray to generate steam, and bake for 25 minutes at 230 degrees. Then lower the temperature to 180 degrees, and bake for a further 25 minutes.
The result is a slightly sweet sourdough bread with a fluffy crumb - fantastic for savoury or sweet toppings.