Day 1: To begin your starter, mix 50g of the flour with 50g tepid water in a jar or, better still, a plastic container. Make sure all the flour is incorporated and leave, covered with a tea towel, at room temperature for 24 hrs.
Days 2, 3, 4 & 5 : Mix 25g flour with 25g tepid water and stir into yesterday’s mixture. Make sure all the flour is incorporated and leave, covered with a tea towel, at room temperature for 24 hrs.
Day 6: The mix should be really bubbly and giving off a strong smell of alcohol. A teaspoonful of the starter should float in warm water if ready. If not, continue adding 25g flour and 25g tepid water into the mixture daily until it becomes active.
If your jar is becoming full, spoon half the mix out of the jar and continue. You now have rye starter, which is a malty flavoured base to sourdough bread. Keep it in the fridge (it will stay dormant) and 12 hrs before you want to use it, spoon half of it off and feed it with 100g flour and 100g water. Leave, covered, at room temperature.
Tip 100g of the starter into a bowl and add 400g of tepid water. Whisk or rub the two together with your hands, don’t worry if there are a few lumps. Add the flour and bring together (with a spatula or your hand) into a thick, sticky dough, making sure all the flour is mixed in, including any dry bits on the sides of the bowl. Cover with a damp tea towel and leave at room temperature for 2 hrs.
Work the salt into the dough then leave, covered, for another 2 hrs.
Heavily butter a 900g loaf tin. Dust the work surface with more rye flour, then scrape all the dough out. Mould the dough into a block roughly the same size as the tin and sit it in the tin. Press the dough down so it fills it completely and scatter the top generously with more flour. Leave the loaf out, uncovered, for 2 hrs until it’s risen by about a quarter and gone craggy on the top, or leave it in the fridge, uncovered, overnight. This will give it an even deeper flavour.
Heat the oven to 230/210C fan/gas 8 with a shelf in the middle of the oven and a shelf below with a roasting tray on it. Put the loaf on the middle tray and carefully pour a small glass of water into the roasting tray. Cook for 50-55 mins until hollow sounding when tapped. (The middle of the loaf will read 98C on a digital thermometer when ready.) Remove the tin and leave to cool on a wire rack for at least 4 hrs. Will keep for 3-4 days in an airtight container.