In a mixing bowl, combine the mashed banana, starter, water, brown sugar, and vanilla, stirring until well mixed.
Incorporate the bread flour and sea salt into the mixture, stirring until there are no dry spots left.
Cover the bowl and let the dough rest for 1 hour.
After the resting period, perform four sets of stretch and folds, spaced about 30 minutes apart, adding chocolate chips during the third set.
Allow the dough to fully ferment until it becomes jiggly, pulls away from the sides of the bowl, and feels non-sticky.
Preshape the dough and let it rest for a few minutes.
Shape the dough for the final time and place it into a banneton for an overnight cold proof in the refrigerator.
