1. In a medium bowl, place 113g unfed mature sourdough mother from the fridge. Let sit at room temperature for 1 hour. Add 128g unbleached bread flour + 48g H20. Combine. Lightly knead for about 2 minutes to form a cohesive ball. Place in a lightly oiled bowl to prevent sticking. Lightly cover. Leave at room temperature to mature for 3 hours. You should start to see air pockets when it is about doubled in size. Fully cover and refrigerate overnight.
2. Pull your levain from the fridge. Meanwhile, autolyse the flour by combining the 500g unbleached bread flour and the 397g warm H20 just until combined. Cover. Let this and the levain sit for 1 hour at room temperature.
3. Add 100g Buckwheat Flour and 14g molasses to the autolysed flour mixture. Tear the room temperature levain into about 12 pieces. Add to the autolysed mixture. Use a mixer with the dough hook attachment on medium low speed for 5 minutes. Turn the dough onto a lightly floured work surface. Let the dough rest for 5 minutes. Add 14g sea salt. Knead by hand for 5 minutes until the ball is smooth, but still slightly sticky. Divide the dough into two equal parts. Place each in a lightly oiled, smooth-sided container (8x8 Pyrex works well). Cover.
4. Stretch & Fold sessions every 20 minutes (80 minutes total) for each loaf: Wet your fingers. Pull the dough to the center. Rotate the container one-quarter turn & repeat. Keep rotating for 4 total folds (until you have come full circle). Cover again and let sit.
Place each covered container in your oven on ‘Proof’ (or in a warm area about 80-90 degrees F) to ferment for about 3 hours (or until doubled).
Cold Retarded Fermentation
Cut your parchment paper handles for each loaf pan & sprinkle with cornmeal or flour to prevent the loaf from sticking. Lightly shape your loaves. Cover. Place in the refrigerator overnight (about 10-12 hours).
Place your baking vessels (you’ll want lots of room for the bread to grow out and up with a lid - typically a cast iron dutch oven) with top in the oven. Turn it on to 500 degrees F for 1 hour.
At 1 hour, remove the loaves from the fridge, sprinkle with flour, use a lame or razor blade or sharp knife to score your desired pattern and your main cut (~45 degree angle in the center or just off-center).
Place each in the hot baking dish with a spritz of water. Immediately return the top to the vessel. Place in oven. Turn down to 450 degrees F. Bake for about 20 minutes with the top on until light golden brown. Remove the top & bake another 5-10 minutes until medium brown.
Remove from vessel to let rest to room temperature before cutting. It will sound hollow when it’s fully baked.