Preheat oven to 350 degrees F. Spread walnuts on a cookie sheet, and bake for 6 minutes, or until they are just fragrant. You can also do this on the stovetop if you prefer. Remove from oven and pour walnuts onto a plate. Toss with cinnamon and let cool.
In a large bowl, mix starter, water, and honey. Add flours and salt, stirring with a fork to combine. Then use your hands to combine until dough is shaggy and flour is worked into dough. Cover with damp cloth and let rest for one hour.
After one hour, perform two stretch and folds, 30 minutes apart. Wait another 30 minutes, then gently stretch and fold walnuts into dough. Cover with damp cloth and let rise until doubled, about 7-8 hours at 70 degree F temperature. Will take longer if it is cooler in your home.
Turn dough out onto a lightly floured surface and let rest for 20 minutes. Then gently fold shape into a circle, pulling the dough towards you to create tension. Place into lined banneton, seam side up.
The second rise can happen on the counter, or if it works better for your schedule, overnight in the refrigerator. On the counter it will take about 90 minutes for the second rise, until it has slightly risen and dough is a bit jiggly. If you do the second rise in the refrigerator, remove it in the morning when your oven is preheated. It will have risen properly by then.
Preheat oven to 450 degrees F. Turn dough out on a piece of parchment paper, gently, and score fairly shallow, as to not disturb the walnuts inside. Place loaf into dutch oven and cover.
Bake for 20 minutes, then remove cover and bake for another 30 minutes.
Remove loaf from oven and place on a cooling rack. Slice and enjoy once fully cooled, at least an hour after removing from oven.