In a large bowl, stir together starter, water, honey, and pumpkin purée. Add flour and salt, then mix until no dry flour remains. Cover and rest for 1 hour.

Perform 3–4 sets of stretch and folds every 30 minutes over 2 hours. Keep covered between sets.

Cover and let the dough rise at room temperature until airy and bubbly, which can take between 3 to 12 hours depending on temperature.

Turn the dough onto a floured surface and gently stretch it into a rectangle. Sprinkle half of the cinnamon-sugar mixture evenly across most of the surface, leaving a small border around the edges. Fold each long side of the dough inward toward the center, without overlapping. Sprinkle the remaining mixture evenly over the top of the folded dough.

Starting at one short end, roll the dough up tightly into a log. Pinch the seams to seal in the filling. Shape the log into a round or oval loaf and place it seam-side up in a floured banneton. Cover and let rest for 30–60 minutes, then refrigerate for 4–24 hours.

Preheat your oven to 450°F (230°C) with the Dutch oven inside. Flip the dough onto two overlapping pieces of parchment paper. Make one clean score down the middle or along the side. Carefully lower the dough into the hot Dutch oven, cover, and bake for 30 minutes.

Remove the lid, reduce the oven temperature to 425°F (218°C), and bake for another 15 minutes, or until the crust is golden brown.

Let cool at least 1 hour before slicing.