This is how I make it:
Starter is 1 part plain flour to 1 part water. When I feed it I use 100g starter, 200g flour, 200g water and leave covered at room temp for about 12 hours Usually when I feed it I keep some and make bread with some. For my usual 2 loaves I do:
To make the levain:
126g strong white bread flour (I use Matthews Cotswold or Doves Farm)
6g wholemeal flour
54g of just fed starter
Mix, leave 12 hours
To make the bread:
772g strong white bread flour, 500g room temp water, 20g table salt, all the levain made previously
Mix it all up until well incorporated in the bowl. Leave 45 mins, fold all sides of dough inwards, Leave 45 mins, fold all sides of dough inwards, Leave 45 mins, turn out onto floured surface, cut in half, gently flatten dough then shape into ball, cover with bowl, leave 20 mins, flip dough ball, gently flatten dough then shape into ball, place in well floured banneton, cover and place in fridge for 12 hours.
Preheat oven and dutch oven too 250C. Allow dough half an hour our of the fridge. Drop dough into dutch oven (I never mastered this - I flip the banneton onto greaseproof paper and lower that into the dutch oven and leave it - I failed at dropping it centrally a couple of times and wasn’t enjoying practicing/failing with something which took me so long to make). Cut slit in top of dough, cook for 20 mins covered + 15 mins uncovered.
I have experimented with shorter / fewer of the wait+fold intervals without noticeable change in the final product. I have also experimented with using 30% wholemeal flour. This seems fine, but it’s just not as nice and I recently chose to be influenced by something i read on the internet about how the starter eats a lot of the simple carbs and therefore sourdough whtite bread is more of a ‘complex carb’ food than standard white bread.