Begin making the dough after the levain has risen (ie, it has doubled in height); for me, this is 8 to 10 hours after feeding (using a glass jar is helpful so you can mark the starting point and easily visualize the rise)
In a large tub/bowl (I use a 6 gallon plastic food-grade tub), combine 700 g of 80 degree water and mix in 200 g leavin; mix well
Add the whole wheat and all purpose flours and combine well into a shaggy mass with no bits of flour showing
Cover and let rest for 40 minutes
Add 50 g of water, and 20 g of salt, and squish to combine.
Set the container in a warm area (78 to 82 degrees) (if wintertime, in oven with hot pan of water or next to stove near a pot of simmering water) for 3 to 4 hour bulk rise, and cover.
During the bulk rise, perform of stretch and folds each 30 minutes. During the last hour, if needed, take care to fold more carefully so not to deflate the dough (I only perform 3 to 4 folds, during the first 2 hours and let the dough rise untouched during the last hour).
After the dough has sufficiently proofed (20 to 30% rise), gently scoop the dough onto an un-floured countertop
Divide the dough into 2 pieces, and lightly flour the top of each. Gently flip over and fold the dough (bottom up and top down) so that the floured surface is envelopes the loaf and then gently preshape into a round boule
Let rest for 20 minutes. The edges should be round and thick (it's ok if it flattens a bit) but they should not taper off. If they do taper or flatten off, preshape again and let sit for another 20 minutes (this is equal to doing another set of folds during bulk rise)
Final shaping (fold the dough into boules [Fold bottom third up, right side third over, left side third over, top third over and then roll the entire loaf over and gently pull toward you letting tension form the loaf further) and then place seam side up into bannetons which have been floured with a 50/50 mix of all purpose and rice flour)
Final rise for 3 to 4 hours at 75 to 80 degrees or place in refrigerator for up to 12 hours (I always do the final proof in refrigerator) (if you do the final rise on counter, do the finger dent test to test for readiness)