In a large mixing bowl, combine the active sourdough starter, warm water, bread flour, and salt. Mix until no dry flour remains and a shaggy dough forms. Cover loosely and let rest for 1 hour.
While the dough rests, cover the raisins with hot water to rehydrate. Drain well before using.
Add one-third of the raisins to the dough during each of the three sets of stretch and folds, resting 45 minutes between each set. After the final stretch and fold, let the dough rest for another 45 minutes.
Turn the dough onto a clean countertop without adding flour. Cover with a towel and let it rest for 10 minutes.
In a small bowl, mix together the softened butter, brown sugar, cinnamon, and flour to make a spreadable paste.
Gently stretch the dough into a rectangle. Spread one-third of the cinnamon butter mixture over the dough, leaving a 1-inch border. Fold one-third of the dough over the center, spread half of the remaining filling, fold again, then spread the remaining filling before completing the final fold into a log.
Pinch the ends closed, then shape the dough into a tight boule by gently tucking the edges underneath and creating surface tension.
Place the loaf seam-side up into a lightly floured banneton or towel-lined bowl dusted with rice flour. Cover and refrigerate overnight for a 12–24 hour cold proof.
The next day, place a Dutch oven in the oven and preheat to 450°F. Once preheated, leave the Dutch oven inside for an additional 30 minutes.
Turn the chilled dough onto parchment paper, score the top with one deep slash, and carefully transfer it into the hot Dutch oven.
Bake covered for 40 minutes. Remove the lid, reduce the oven temperature to 425°F, and bake for another 3–10 minutes until deeply golden.
Transfer the bread to a wire rack and cool completely for at least 2 hours before slicing.