In the morning, combine 50g of your unfed starter with the whole wheat flour and warm water in a clear container with straight sides and mix until no dry flour remains. This is your levain. Mark the height with a piece of tape or erasable marker.
Place the levain into a warm area like the oven with the light on and the door cracked, on top of the fridge. A warm area is between 72ºF-95ºF. Starter will die if the temp rises above 130ºF
Let your levain rise until it has reached its peak (the highest point in its rise before it starts to fall again). I track this by checking my levain hourly. If your levain doubles in size within 5 hours you can use it to make bread. If it doesn't your starter isn't strong enough yet or your room is too cold.
While the levain is rising, make the autolyse (mixture of flour and water before adding the levain).
Once your levain has peaked, add 140 grams to the autolyse. This is pretty much the whole container minus whatever is stuck to the sides. Also add in the salt and then mix it all together with your wet hands. Pinch, fold, push with your fingers until it's all cohesive and evenly mixed. Cover it with plastic wrap and let it rest for 30 minutes.
Begin your first stretch and fold. With a wet hand, lift one side of the dough and pull it to the point of resistence but don't tear it. Fold it over the top of the dough. Rotate the bowl 45º and repeat the stretch and then fold the dough over. Do this for a total of 4 times. Cover the dough with plastic wrap and let it rest for 60 minutes in a warm area.
After 60 minutes, begin your second stretch and fold. The same process as the first stretch and fold. Cover and rest 60 minutes in a warm area.
After another 60 minutes, begin your third stretch and fold. Same process. Rest for 60 minutes. If the dough still feels really loose then you may want to do a fourth stretch and fold.
After your stretch and folds are complete, cover your dough and let it rise for 1-2 hours until it has doubled in size. This can take even longer than 2 hours if your room is cold or your starter is weak so don't rush it and just wait until the dough is ready.
Once your dough has doubled you can shape it. Take your wet hand and get the countertop a little wet. This prevents sticking. Gently pour the risen dough onto the counter and stretch it out into a rectangle horizontally in front of you, about the size of a sheet of paper. Pop any big bubbles just as you would if you were making regular bread. Big bubbles make problems in the bread later.
Fold the right side of the dough over itself so that the right edge lines up with the center of the dough. Now take the left side of the dough and fold it over the top. This is called a simple book fold and helps distribute the bubbles more evenly in your final loaf so all your bubbles aren't on the top or bottom.
Now roll the dough up like a cinnamon roll. Nice and tight. This helps make that gluten even stronger so our bread can rise in the oven. Make sure the seam is on the bottom. Cover the dough with the bowl and let it rest for 15 minutes.
While the dough is resting, prepare your banneton. Dust on some flour generously. You can also use a bowl with a tea towel and it works just as well.
Turn your dough over so the seam is facing up. Gather all the edges together and lift the dough like a bag and plop it into your floured banneton. Pinch together any loose edges.
Place the whole basket into a plastic bag to keep it from drying out and put it into the fridge overnight. The dough will not rise or do much of anything in the fridge. It's like a pause button for sourdough so make sure all your shaping and rising is done before going into the fridge.