Mix the apple cider and starter, then add the bread flour and salt. Mix until combined and rest for 1 hour.
Do 4 sets of stretch and folds, 30 minutes apart.
Let the dough bulk ferment until it is jiggly and no longer sticky to the touch.
For the apple mixture, cook the diced apples with the butter, brown sugar, vanilla, cinnamon, and salt until softened. Let the mixture cool completely before adding it to the dough.
Stretch the dough out for lamination and spread the cooled apple mixture over the dough. Fold the dough up, shape, and place in a floured banneton.
Cold proof until ready to bake.
Preheat oven to 450°F. Score the loaf and bake covered for 40 minutes.
Remove the lid and bake uncovered for another 10 minutes, or until the internal temperature reaches 205°F.
Cool for at least 1 hour before slicing.
