Start by blooming the cocoa powder. In a large bowl, mix the cocoa powder with hot water and whisk until fully absorbed. Let it rest for two to three minutes to cool slightly.
Combine the cooled cocoa mixture with the remaining water. Add the active sourdough starter (or chocolate sourdough starter if using one), brown sugar, white bread flour, and fine sea salt, then stir until a shaggy dough forms.
Cover the bowl and let the dough rest for 45 minutes to one hour to allow the flour to hydrate.
Begin the stretch and fold process by performing four sets of stretches and folds, spacing them 45 minutes to an hour apart. After each fold, rotate the bowl 90 degrees and cover it well to prevent drying.
Allow the dough to bulk ferment at a temperature of 21–23°C (70–73°F) for about ten hours, or until it rises by 85%. If you're baking during summer, or if your kitchen is warmer (over 27°C/81°F), reduce the bulk fermentation to six/seven hours and/or limit the rise to 70% to prevent overproofing.
When the dough has completed bulk fermentation, shape it by gently stretching it into a rectangle. Add half of the chocolate and almonds, then fold the dough like a letter. Add the remaining add-ins during the next folds, finishing by rolling the dough into a semi-ball. Use your hands to pull the dough toward you to create tension, repeating this process on all sides.
Place the shaped dough into a prepared banneton. Using rice flour will prevent the dough from sticking—wheat flour does not have the same effect! Cover it well and refrigerate overnight or for up to 36 hours.
When ready to bake, preheat the oven to 500°F (260°C) with a rack positioned in the middle.
Remove the dough from the refrigerator and place it in a cold Dutch oven lined with parchment paper. Score the top to control expansion during baking using a sharp blade. For this bread, I score making an "X" on the top.
Lower the temperature to 450°F (232°C) and bake with the lid on for 30 minutes. After 30 minutes, remove the lid, lower the temperature to 425°F (218°C), and bake for an additional 20 to 25 minutes, until the internal temperature reaches at least 195°F (91°C).
Once baked, allow the bread to cool for at least one hour before slicing. Cutting too soon may result in a gummy crumb.