Mix bread flour, whole wheat flour, active sourdough starter, water, pumpkin puree, maple syrup, pumpkin pie spice, and cinnamon in a mixing bowl until no dry flour remains. Rest for 30 minutes at room temperature so the dough hydrates and looks smoother.

Add salt and mix thoroughly until fully incorporated and the dough feels cohesive. Perform 4 sets of stretch and folds, letting the dough rest 30 minutes between each set until it visibly strengthens.

Bulk ferment at room temperature for 4-6 hours until the dough is roughly doubled and bubbly throughout. You should see active fermentation bubbles forming under the surface.

Shape the dough into a boule or batard and place it seam-side up in a floured banneton. Lightly coat with rice flour for shaping so the dough releases without tearing.

Refrigerate overnight (8-12 hours) for a cold proof. The dough should look slightly puffy and aerated when you remove it.

Preheat the oven to 500°F with a Dutch oven inside for 45 minutes. The pot should be very hot so the loaf springs and forms a crust quickly.

Carefully score the top of the cold dough right before baking, using confident shallow cuts. The surface should open slightly as it bakes, showing where the loaf will expand.

Bake covered for 20 minutes at 500°F in the preheated Dutch oven. The loaf will begin to rise and set, and condensation will help create oven spring.

Uncover and bake 20-25 minutes longer at 500°F until deeply golden. The crust should look dry, firm, and intensely colored.

Cool the bread completely on a wire rack before slicing. Letting it cool prevents gummy crumb and helps the crust crisp as it sets.