1. 1. Combine Starter and Water: In a large mixing bowl, gently whisk together your active sourdough starter and warm water until the starter is mostly dissolved and bubbly. This ensures even distribution throughout the dough.

2. 2. Mix Dry Ingredients: In a separate bowl, whisk together the bread flour, unsweetened cocoa powder, granulated sugar, and fine sea salt. Make sure there are no lumps in the cocoa powder.

3. 3. Form the Dough: Add the dry ingredient mixture to the wet starter mixture. Use your hands or a sturdy spatula to mix until all the flour is hydrated and a shaggy dough forms. Cover the bowl with a clean kitchen towel or plastic wrap and let it rest for 30 minutes (this is called autolyse, and it helps the flour absorb water).

4. 4. Incorporate Inclusions: After the rest, sprinkle the chocolate chips and toasted chopped hazelnuts over the dough. Gently fold them in, ensuring they are evenly distributed. This might take a few minutes of squeezing and folding the dough.

5. 5. Perform Stretch and Folds: Over the next 2-3 hours, perform 3-4 sets of stretch and folds every 30-45 minutes. To do this, lightly dampen your hands, grab a portion of the dough from the edge, stretch it upwards, and fold it over the center. Rotate the bowl and repeat 3-4 times per set. This builds strength in the dough.

6. 6. Bulk Fermentation: After the stretch and folds, cover the bowl and let the dough bulk ferment at room temperature (around 70-75 F) for 4-6 hours, or until it has visibly increased in volume by about 30-50% and looks bubbly. The exact time will depend on the strength of your starter and your room temperature.

7. 7. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Shape it into a round or oblong loaf, being careful not to degas it too much. Place the shaped dough into a floured banneton or a bowl lined with a floured kitchen towel, seam-side up.

8. 8. Proofing and Baking: Cover the banneton/bowl and place it in the refrigerator for 2-4 hours for a shorter cold proof, or 8-12 hours (or overnight) for a deeper flavor development. Preheat your oven to 450 F (232 C) with a Dutch oven inside for at least 30 minutes. Carefully transfer the cold dough from the banneton into the hot Dutch oven, score the top with a sharp blade, and bake covered for 25 minutes. Remove the lid, reduce the temperature to 425 F (218 C), and bake for another 20-25 minutes, or until the crust is deep golden brown and the internal temperature reaches 200-210 F (93-99 C). Let it cool completely on a wire rack before slicing.