In a large bowl, mix bread flour, whole wheat flour, active sourdough starter, water, pumpkin puree, maple syrup, pumpkin pie spice, and cinnamon until no dry flour remains; then cover and rest 30 minutes at room temperature (autolyse). During the rest, the dough should look slightly smoother and feel hydrated.

Add the salt and mix thoroughly until fully incorporated, then let the dough rest 30 minutes at room temperature. Perform 4 sets of stretch and folds, one set every 30 minutes.

For each stretch-and-fold set, gently stretch the dough up and fold it over itself, rotating the bowl about 90° between folds. After the final set, the dough should feel tighter and hold shape better.

Cover and bulk ferment at room temperature for 4–6 hours until doubled and visibly bubbly. The dough is ready when it looks airy and you see bubbles across the surface.

Shape the dough into a boule or batard, then place it seam-side up in a banneton dusted with rice flour for shaping. The surface should be smooth and well-tensioned during shaping.

Refrigerate overnight for a cold proof of 8–12 hours. The dough should feel puffy but still cool when you remove it to bake.

Preheat the oven to 500°F with a Dutch oven inside for 45 minutes. The pot must be hot so the loaf springs right away.

Carefully turn the dough out onto parchment and score the top, then place it into the hot Dutch oven and cover. Keep the loaf seam side up as it goes into the pot.

Bake covered at 500°F for 20 minutes until the crust color starts to set and expand. You should see significant oven spring and a firming surface.

Uncover and bake at 500°F for 20–25 minutes more until deeply golden. The loaf should look caramel-browned with darker edges.

Remove the bread and cool completely on a wire rack before slicing. Letting it cool fully prevents a gummy interior and helps the open crumb set.