1. The fig water takes between 5 and 7 days to ferment. It is nothing else but wild yeast born in water fed on sugars provided by the fruit. Use any fruit with reasonable sugar content, as long as it’s untreated, without preservatives or oils, and unwashed.
2. Place the figs in a large (1l) jar or tub with a lid. Add a cup of lukewarm water, shake the contents and leave in a warm place for 24 hours. Add another cup of water, give it a shake and leave for up to 6 days. Shaking the jug once a day is not strictly necessary but you might want to inspect your wild yeast bubbles forming daily.
3. The fruit needs to have floated up to the surface and the chunks to be covered in tiny bubbles. The smell will be quite sharp and hooch-like when you open the lid, but once it dissipates there should be a pleasant fruity aroma coming from your water. It won’t keep and can’t serve as a further fed starter (at least not in my experience) so you need to use it straight away.
4. To make the sponge, place the rye flour and half the strong flour in a bowl. Strain the fig water and add 280g of it to the flour. Mix to a shaggy dough. Cover the bowl with cling film and leave in a warm place for an hour.
5. Add the remaining flour and the 100g fig water and start kneading in a standing mixer with a dough hook attachment or by hand. When the dough comes together add the salt and continue kneading or mixing until the dough is smooth, elastic and clears the bowl or stops sticking to your hands.
6. Return it to the bowl. For the next 2-3 hours (depending on the ambient temperature and how quickly the dough will revive), every 30 minutes pick the dough from the bowl with oiled hands and stretch and fold it on itself until it resists to stretch any more. Put it back in the bowl and cover. At the end of this exercise the dough should be significantly smoother and springier.
7. After the last stretch and fold leave the dough on the worktop to rest for 15 minutes, covered with a clean tea towel.
8. Pre-shape the loaf: fold edges inwards to form a rough ball; let it rest again, seam side down, under a tea towel for 10 minutes. Prepare a proving basket or a bowl lined with a clean, thickly floured cloth.
9. Shape a round loaf: flatten the dough to a disc. Lifting the edge close to you, roll it away until you get a fat sausage. Flip it seam side up and roll in the opposite direction into an even fatter sausage. Flip it seam side down, cup its far side with your both hands and gently drag it towards you. You’ll feel the top smoothing and tightening. Turn it 90 degrees and drag it towards you again. If the dough sticks, flour your hands lightly.
10. Place it in the floured proving basket seam side up, cover the basket with a plastic bag and leave at room temperature for an hour. Then place it in the fridge for 12 – 18 hours; it will bake from cold.
11. When you’re ready to bake, preheat a Dutch oven or a cast iron casserole (about 20cm diameter) in the oven heated to 220C/425F/gas 7. Remove the dough from the fridge, take the Dutch oven carefully out and turn the dough out of the basket into it. Shake the dish about to centre the dough and slash the top with a wet knife or blade.
12. Bake it for 20 minutes with the lid on and for further 20 without the lid until it’s deep golden brown and looks very crusty. Cool for 30 minutes in the dish, then turn it out onto a wire rack.