Feed your sourdough starter about 4–6 hours before baking, until it’s bubbly and active.
In a large mixing bowl, whisk together bread flour and cocoa powder until evenly combined.
Add warm water, active starter, and brown sugar. Mix until no dry flour remains. Let rest for 30 minutes (autolyse stage).
Add salt and mix again using your hands or a dough hook until incorporated. Perform a few stretch and folds over 2–3 hours, letting the dough rest 30 minutes between each set.
During the final fold, gently mix in chocolate chips, vanilla extract, and any optional add-ins (nuts, dried fruit, espresso powder).
Cover the bowl and let the dough bulk ferment at room temperature (75°F / 24°C) for 4–6 hours, or until nearly doubled in size.
Turn the dough out onto a lightly floured surface. Shape into a round loaf using a bench scraper, then transfer to a proofing basket dusted with cocoa or rice flour.
Cover and cold-proof the dough in the refrigerator overnight (8–12 hours). This deepens flavor and strengthens structure.
Preheat your oven and Dutch oven to 450°F (230°C) for at least 30 minutes before baking.
Place the dough (on parchment paper) into the hot Dutch oven. Score the top with a lame for expansion.
Bake covered for 25 minutes, then uncover and bake an additional 15–20 minutes until the crust is dark brown and crisp. Internal temp should reach 205–210°F (96°C).
Cool the loaf completely on a wire rack before slicing to prevent a gummy texture.