First, mix starter, bread flour, water, cocoa powder, sugar, vanilla and salt.

Combine well, using hands to mix as needed. Dough will be sticky and soft.

Let dough rest for 30 minutes, then do your first stretch and fold. Add chocolate chips in with these stretch and folds. Example: Add 1/4 of chocolate chips, stretch and fold. Add another 1/4 of chocolate chips, stretch and fold. Repeat until all chocolate chips have been added with those first stretch and fold.

Complete 3-4 rounds of stretch and folds, every 30 minutes. Cover dough between rounds.

Let dough bulk ferment for 4-8 hours (starting from when dough was mixed).

Fermentation is complete with dough is risen around 40% and is slightly puffy, domed and bubbled on top.

Once fermentation is complete, shape your loaf and place into banneton.

Cold ferment in refrigerator for 6-12 hours.

Before baking, score loaf and transfer to hot Dutch oven.

Bake at 450 degrees F for 50 minutes (covered).

Let cool completely (at least 1-2 hours) before slicing and serving.