We have used this recipe to bake bread for many many years! Hope you find it helpful.
500g T65 Flour (strong French-Swiss flour often used for making baguettes)
150g sourdough starter (the one we have is over 70 years old!)
500g of flour and 320g of water.
Leave it with a wet towel over the top for at least an hour.
Add 150g sourdough starter and the remaining water (30g) and knead.
Put some olive oil on the top and bottom to stop it sticking. The sourdough will then go through the autolyse. The sourdough is actually feeding and using the carbohydrates in the flour to produce ethanol and carbon dioxide. Ethanol is converted by the bacteria, producing lactic acid. Bubbles of carbon dioxide become trapped in the stretchy dough, making it rise.
Cover with a wet towel and after 20 minutes add salt.