In the morning make your dough combine 2 tablespoons (15-20 grams) of unfed sourdough starter with 85g of water 60 g of bread flour, and 25 g of whole wheat flour. Mix until there are no dry bits of flour, cover loosely with plastic wrap and let sit out for 4-5 hours or until it doubles in volume.
While leavain is getting ready, autolyse the flour, mix bread flour, spelt and whole wheat flour with water and set aside. You can give at least 1 to maximum of overnight if you want.
Once leavain is ready mix in with the autolyzed dough and set aside for 30 minutes.
. After the 30 minutes is up add salt. Mix well and cover the dough again.
Then turn the dough every 30 minutes for until 1hours. This means grabbing the underside of the dough and stretching it up and over the rest of the dough. Perform a few of these turns each time you handle the dough.
After an hour, divide the dough into to two and incorporate purple sweet potato into one half of the dough. Set aside for another 1 hour.
After one hour do a lamination of the dough. Means spread the dough into thin sheet and fold them into a letter fold.
After 1 ½ hours is up, let the dough rest for hour interval before you turn it again.
Then transfer the dough lightly floured workspace and shape them into round like this. Fold the third of the dough closest to you inward, and then stretch the dough out to the sides. Fold the right, and then left sides in toward the center. Fold the top of the dough inward, and then wrap the bottom part of the dough over it all. Work this into a round shape, and place seam side up in a proofing basket lined well with flour.
Let rise overnight in the refrigerator.
When you are ready to bake preheat oven to 475°F.
Remove the dough from the proofing basket and score the dough then transfer to Dutch oven and close the lid and immediately place the top back on and return to the oven.
Bake at 475F for first 15 minutes
Turn the heat down to 450°F and cook for 15 minutes.
After 15 minutes remove the top of the Dutch oven and rotate the pan. Continue to bake the bread for another 15 minutes, until the crust is deeply caramelized.