Feed Starter Night Before. In a cup, bowl, or pint mason jar, add 30 grams of sourdough starter, 35 grams of unbleached all-purpose flour, and 35 grams of room-temperature filtered water. Stir to combine fully. This will give you 100 grams of starter.
Make the Dough. Add the active sourdough starter and water to a large mixing bowl. Using a whisk or wooden spoon, stir to mix the starter into the water. Add the salt and all-purpose flour to the bowl and stir to combine.
Rest. Once everything is mixed together, cover the bowl and allow the mixture to sit for 30 minutes.
Stretch and Fold. After 30 minutes, wet your hands with water (this prevents the dough from sticking to them). Pick up one corner of the dough, stretch it up, and fold it over itself. Then, turn the bowl about a quarter of a turn and repeat this process three or four times.
Rest. Once you’ve finished the stretch and folds, cover the bowl again and allow it to sit for 30 minutes.
Repeat. Repeat the stretch and fold process 3-4 times, with 30-minute rests in between. (With each stretch and fold session, you will notice the dough becoming stronger and stretching further. This process develops the gluten. You will know the dough is ready for its bulk rise when it is soft, smooth, and pliable.)
Rise. Once the stretch and folds have been completed, cover the bowl and store the dough in a warm place for 12 hours or until it has almost doubled in size.
Prepare Banneton. Liberally flour your banneton or proofing basket with all-purpose flour, then set it aside.
Roll Out Dough and Add Raspberries and Chocolate. After the dough has risen, turn it out onto a clean, dry surface. Lightly roll the dough out into a rectangular shape. Sprinkle with some sugar, raspberries, and white chocolate chips over the dough.
Fold Dough and Continue to Add Raspberries and Chocolate. Fold the dough, leaving ⅓ open. Then fold the remaining ⅓ over. Turn the dough and sprinkle the remaining raspberries and white chocolate chips over the surface.
Roll the Dough into a Ball. Roll the dough up so it is about the same shape and size as your banneton.
Place the Dough In a Banneton and Refrigerate. Place the dough, smooth side down, into your banneton. Cover and refrigerate for 8 hours.
Let Dough Come To Room Temperature. Remove the dough from the fridge and allow it to come to room temperature (about 2 hours).
Prepare Oven. 1 hour 15 minutes after pulling the dough from the fridge, preheat the oven to 450 degrees F (232 C) with your Dutch oven inside on the bottom rack.
Score the Dough. 10 minutes before you’re ready to bake, turn the dough onto a silicone bread mat or parchment paper. Using a razor or knife, cut a slash on the dough. This will help keep the shape of the bread and allow it to rise while baking.
Bake. Place the dough in the preheated Dutch oven. Add 3-4 ice cubes tucked between the parchment paper and Dutch oven. Bake at 450 degrees F (232 C) for 25 minutes with the lid on. After 25 minutes, remove the lid, reduce the heat to 375 degrees F (190 C), and bake for 25 minutes.
Cool. Remove the bread from the oven and let it cool on a cooling rack for 30 minutes before cutting into it. (Cutting into the bread too soon will cause your bread to look doughy.)