• Mix together the starter ingredients in a bowl and stir well until thoroughly mixed. Add it to a clean jar and loosely cover it. Leave it in a warm spot until it doubles in size.
• When the starter has almost finished rising, combine the bread flour, water, orange juice, orange zest and sugar in a large mixing bowl. Use a fork or wooden spoon to bring it together, then switch to wet hands to mix it into a shaggy dough ball with no dry bits of flour remaining. Cover the bowl and let it autolyze at room temperature until the starter is ready.
• Add the starter to the dough and squish it in using wet hands. Add in the salt and mix it in. Add in a few slap and folds to incorporate it better and start developing the structure.
• Over the next 3 hours, stretch and fold this dough every 30 minutes. Pull the dough up and over itself, turn the bowl a quarter turn, and repeat. Do this on all sides, and always use wet hands.
• After the last fold, let the dough rest for 20 minutes, then pull it out of the bowl using wet hands, onto a bench lightly wetted with water. Stretch it into a rectangle and spread on half the chopped chocolate. Fold the dough like a pamphlet to trap the chocolate, then add on another layer of chocolate. Roll it up into a log, then shape it into a ball with the palms of your hands, rolling it on the bench and creating a bit of surface tension as you roll.
• Place it back in the bowl and give the the dough another hour or two to finish the bulk proof. There should be definite signs of activity on the dough, like bubbles forming and the dough will jiggle if you give the bowl a shake. In a room temperature of around 24°C/75°F my dough needs about another 1 1/2 hours, but in colder temperatures it will take longer.
• Shape the sourdough into a batard or ball depending on what basket you’re using.

Shaping a Batard

• Line a banneton basket with a kitchen towel and flour it well.
• Tip your dough carefully on a lightly floured work surface and gently form it into a rectangle.
• Take the bottom third of the dough and fold it up so it meets the middle. Take the right side of the dough and fold it to meet the middle.
• Then, take the left side of the dough and fold it into the middle.
• Bring the top third of the dough down to the middle to create a little dough packet.
• Now add some stitches down the dough by grabbing some dough from the top left and a little from the top right and bringing them together to meet in the middle.
• Carry on doing this down the length of the dough. When you reach the bottom, grab a flap of dough and carry it over the stitched dough to meet at the top. This will create a log.
• Now, gently grab this log and roll it gently towards you on the bench. This will create some surface tension. All the while, take care not to de-gas your dough too much.
• Place the shaped dough in the floured basket, seam-side up.
• Cover the dough with a kitchen towel and cold-proof in the refrigerator for 8-24 hours.

Baking

• The next day, preheat the oven and a Dutch oven to 450°F/230°C for at least 30 minutes until well-heated.
• Remove the hot Dutch oven and flour the bottom well. Take the dough from the fridge and carefully flip it out of the basket and into the Dutch oven. If baking this in a large pot, it's best to tip your dough onto a piece of parchment paper. This way, you can lower it into the pot.
• Score the dough using a razor blade or sharp knife.
• Bake covered with the lid for around 20 minutes. Remove the lid and bake uncovered for 20 minutes more, depending on your preference or your oven. Some ovens run hotter and may need less time, while others need more.
• Let the sourdough cool for at least two hours before slicing.