Mix. In a large bowl, combine the water, active sourdough, and sugar and stir to combine.
Add half the bread flour. Add half the bread flour to the bowl and stir until well incorporated.
Add salt and bread flour. Add the salt and the rest of the flour, and use a spatula to mix until everything comes together. Cover with plastic wrap or a tea towel and let it sit for 30 minutes.
Stretch and fold. Uncover the dough and use wet hands (this prevents the dough from sticking) to pick it up. Stretch the dough upwards and fold it back down towards the center. Turn the bowl ¼ of a turn and repeat. Turn and repeat two more times until the dough has been released from the sides of the bowl. Flip the dough over, cover, and let it sit for 30 minutes.
Repeat. Repeat the stretch and fold process 2-4 more times, including the 30-minute rest, until the dough stretches easily and is soft and smooth. This will take about 2 hours.
Add half of the cinnamon and raisins. After your last stretch and fold, it’s time to incorporate the cinnamon and raisins. Sprinkle about half of the cinnamon and raisins over the dough.
Stretch and fold. Stretch and fold the dough to swirl the cinnamon and raisins into the dough.
Add the rest of cinnamon and raisins. Sprinkle the rest of the cinnamon and raisins over the dough and stretch and fold the dough to get everything incorporated.
Roll dough. Roll the dough into a loaf shape, tuck in the ends, and place it in a clean bowl. Cover with plastic or a tea towel.
First rise. Set the dough in a warm place to rise for about 4 hours or until it has doubled in size.
Shape dough. Turn the dough out onto a lightly floured surface. Slightly flatten the dough into a rectangular shape, fold it in the corners, and roll it up, tucking it in the ends.
Bulk rise. Place the dough in a well-floured banneton (you can use a clean bowl if you do not have a banneton). Cover with a towel, plastic wrap, or a plate and place in the fridge overnight.
Prep for baking. One hour before you bake the bread, remove the dough from the fridge and let it warm to room temperature. About 30 minutes before your dough is ready, place your Dutch oven into the oven on the lowest rack and preheat to 450°F.
Score the dough. Place your dough onto parchment paper or a silicone bread mat. Using a bread razor (or a very sharp knife), score the dough vertically along the midline (you can make fun designs at this point).
Bake. Once the oven has preheated, remove the lid from your Dutch oven, add 4-5 ice cubes to the inside, place the dough with the parchment paper into the Dutch oven, and bake it covered for 25 minutes. Reduce the heat to 375°F, remove the lid, and bake the bread uncovered for 20-25 minutes.
Cool. Remove the bread from the oven and let it cool for 20 minutes before cutting into it.