In a large bowl, mix the flour, water, sourdough starter, and salt using a spoon or your hand. No need to knead—just stir until you have a sticky, rough dough. Cover the bowl and let it rest for 30 minutes to hydrate the flour.

After the rest, do your first set of stretch and folds. Wet your hand, lift one side of the dough, and fold it over. Repeat on all sides. Do 2 to 3 total rounds of folds over the next 1.5 hours, spacing them out every 20 to 30 minutes.

After the final fold, cover the bowl again and let the dough continue to bulk ferment until it rises by about 50%. At average room temperature, this usually takes around 6 hours from the time you first mixed the dough.

Turn the dough onto a lightly floured surface. Gently stretch it into a rectangle—not too thin.

Lightly spray the surface with water, or wet your hands and pat the dough to moisten it slightly. Sprinkle about three-quarters of the cinnamon-sugar mixture evenly over the dough, followed by three-quarters of the raisins.

Roll the dough into a log from top to bottom. Then sprinkle the remaining cinnamon-sugar and raisins over the top of the log and roll it up again into a spiral. Tuck the ends under.

Gently shape the dough into a round ball.

Place the dough seam-side up in a floured proofing basket. Cover and let it rise at room temperature for 1.5 to 2 hours, or refrigerate it overnight.

Preheat your oven with a Dutch oven inside. For a conventional oven, preheat to 250°C (480°F). For a convection oven, preheat to 240°C (465°F). Just before baking, turn the dough out onto parchment and make one expansion score. A simple moon-shaped score slightly off-center works well.

Carefully place the dough into the hot Dutch oven, cover with the lid, and bake for 20 minutes. Then remove the lid and reduce the temperature—230°C (450°F) for conventional, or 210°C (410°F) for convection—and continue baking uncovered for another 20 to 25 minutes, until the crust is golden and crisp.

Let the bread cool completely on a wire rack before slicing.