Feed your starter at a ratio of 1:3:3 to ensure you'll have 120g ready to use in the morning.For example, 20g seed starter, 60grams fresh flour and 60g water will give 140g active starter to use in the morning, of which you can take 120g. Ensure your starter has at least doubled, if not tripled (but not collapsed), before using it.
The Next Morning - Mixing The Dough
Your starter should have easily doubled, if not tripled at this point and should still be holding its shape.If it has risen and then sunk (you should see the marks on the jar), it may have risen too quickly overnight and passed its peak. In future your starter can be fed more flour, less seed starter to slow this rise down.In a large bowl combine all the bread ingredients (except for the starter) and mix into a shaggy dough. Cover the bowl with a plate and leave the dough on the bench to hydrate, for 15-30 minutes.
Add the starter to the autolysed dough and mix it well together, then place it into a shallow glass dish.
Every 30 minutes, perform 1 set of coil folds (see video in the post above.) Do this a total of 4 times. In between the folds, keep the dish covered with a plate to stop the dough drying out.
After the 4th fold, leave the dough to sit and rest for a further 30 minutes.
Shaping The Dough
Now, flour your hands and a work bench and tip out the the dough. Gently stretch it out into a square.Take one edge of the square and bring it into the middle, then repeat with the remaining edges and form a ball.With the seams facing up, push the ball out onto the bench, and roll it up like you would a sleeping bag or a Swiss roll.
Place the dough, seam side down into a baking paper lined 450g (or 1lb) loaf tin.
Now leave it to rise in a warm place until has bulked out by 50%. A temperature between 21-25 degrees Celsius is good. If necessary, create a warm spot such as an oven that has been gently preheated (and then turned off.) In a warm spot like this it should take approximately 3-4 hours, but it may take longer in cooler temperatures. It's best to watch the dough and not the clock. During this rise, cover the loaf tin with a dampened tea towel to stop the dough drying out.
Cold Proof
Now the dough is put in the fridge for a cold proof, where the fermentation is slowed down and the flavour is developed.This should be a minimum of 4 hours but it can go up to 20 if you want to bake your bread the following day. I like to bake it that night, so it has cooled by morning and can be sliced for school sandwiches.During the cold proof, cover the loaf tin with a dampened tea towel to stop the dough drying out.
Baking
After the cold proof it's time to bake. Heat the oven to 230°C (210°C if using fan-bake). Once the oven is heated, bake the bread for around 25-30 minutes until dark browned and risen. If you lift the bread out of the tin and tap the bottom it should sound hollow when it's done.
Leave the bread to cool for a minimum of 2 hours before slicing.