Take old dough(from previous mix), make a preferment with it adding
flour and water to it (100 flour, 40 old dough, about 60water) making
it a tight dough.
Leave it for about an hour to proove.
Then mix the main dough, using:
100 flour T80 (a fine wholemeal. If no T80 available, I guess you can
just sieve wholemeal flour)
2 coarse sea salt
30 preferment

Are the numbers grams or baker's percentages?