185g WM Dark Rye starter @100% hydration
560g Strong White Bread Flour (I'm currently using the Shipton Mill Canadian)
240g Wholemeal (just finished a 25kg sack of the 14% stoneground)
40g Wholemeal Spelt
560g water (67% hydration in final dough)
It is essential to use a starter that is fed and active, definitely not straight out of the fridge. What you do to achieve that is a matter for you, but I start with about a tablespoon of discard (actually what is left from previous bake), feed 1:1 at bedtime with 20g wholemeal Rye. 20g water. In the morning add 75g WM Rye and 75g water.
When starter has increased in size by 50%. mix all flours and water in a bowl until everything is well combined. There should be no dry flour but also no kneading. Autolyse until starter has doubled. If your starter is properly active you can wait a little longer if you wish, as long as the starter is continuing to grow. I usually end up between 5-7 hours, depending on the ambient temperature in my kitchen.
When starter has doubled (tripled even) mix salt into dough. Spread round and, with wet hands, keep folding corners of dough over until roughly incorperated. Then add the starter and do the same. Thoroughly mix, then knead until the dough is smooth and elastic using your preffered method. i use the Rubaud method with a wet hand so no additional flour is added.
Cover with an elasticated plastic food cover (or a showercap if you like). Do not use clingfilm. It should be banned. If all else fails use a damp tea towel. I've also used a supermarket shopping bag on occasion. Prove somewhere warm (ideally 27-30 degees celsius), with stretch and folds in the bowl every half an hour x3, then leave until increased in volume by about 50%.
Turn out onto a flat surface, generously flour top, divide in two, then, each half in turn, using a bench scraper flip dough over, stretch and fold L-R and top to bottom. flip back over and roughly shape into a boule. After 15-20 minutes repeat, place into floured bannetons (if you don't have any put a cotton tea towels in mixing bowls and dust with flour), cover with "shower cap" and place in bottom of fridge overnight.
In morning, heat oven to max. Bake in cast iron/dutch oven/cloche for 10 mins. I use a silicon disc anda peel to get the dough into the cast iron without having to take it out of the oven. Slash with a lame or sharp knife before it goes in the oven. Turn down heat to 220C for further 10 mins. Remove cover/lid and bake further 20 mins. Turn off oven, wedge door slightly open with oven glove or similar and leave 5 mins more. Remove from oven and cool on rack. Turn up oven and repeat for second loaf. If you don't have a dutch oven or similar use steam. Plenty of tutorials out there on the web.