Bloom the cocoa by stirring the hot brewed coffee into the cocoa powder until smooth and paste-like.
In a large mixing bowl, combine the bloomed cocoa, sourdough starter, and room-temperature water.
Add bread flour, brown sugar, and salt to the bowl. Mix with a spatula or by hand until a rough, shaggy dough forms.
Let the dough rest for 30 minutes to hydrate and relax gluten.
Perform 3 to 4 sets of stretch and folds every 30 minutes over 2 to 2.5 hours, gently folding in mini semi-sweet chocolate chips during the second and third sets.
Cover the dough and allow it to bulk ferment at room temperature for 6 to 7 hours until nearly doubled and airy.
Transfer the dough to a floured surface and shape into a round or oval loaf, pressing milk chocolate chips evenly into the dough.
Place the shaped dough into a well-floured proofing basket or bowl and proof at room temperature for 30 minutes to 1 hour until slightly puffy.
Preheat the oven to 450°F (232°C) with a Dutch oven inside. Transfer the loaf into the hot Dutch oven, score the top, cover with the lid, and bake for 25 minutes.
Remove the lid and bake uncovered for an additional 15 minutes until crusty and baked through.
Let the bread cool on a wire rack for at least 1 hour before slicing.