Put 500g flour into a bowl and add 300g of your sourdough culture. Then add 250ml warm water and i use 12g salt. Mix it all together and then turn it out onto a table for kneading. It is a wet dough so you have to work it for a while 15 minutes by hand) or i do 500 kneads before it will start to come away from the table. The finished dough should be very soft but doesn't stick to the back of your dry hand. If it does, work in a little more flour.
Once it's stretchy, put it into a bowl and leave it somewhere warm to rise for 2 hours with a tea towel over it
Shape the dough on a lightly floured surface to fit a banetton then I put a shower cap over it and leave it to rise in a warm place for a second time, for about 8 - 12 hours.
To bake it you will need a baking stone or a heavy metal baking tray. Get your oven very hot at 240°C/gas mark 9 and heat the stone or tray and it my oven i bake covered for 20 mins and without cover for a further 20 mins then cool on a wire mesh/tray