The night before baking, combine 50g active sourdough starter with 100g flour and 100g water in a clean jar. Mix thoroughly until no dry flour remains. Cover loosely and leave at room temperature (68-72°F) overnight for 8-10 hours. Your levain is ready when it's doubled in size and shows a bubbly, active surface.
In a large bowl, combine all of your bubbly levain with pumpkin puree and maple syrup, whisking until smooth. In a separate bowl, mix your flours, salt, and pumpkin pie spice. Gradually incorporate the dry ingredients into the wet, mixing first with a spatula and then with your hands until a shaggy dough forms.
Perform 4-6 stretch and folds directly in the bowl at 30-minute intervals during the first 2 hours of fermentation. Simply wet your hands, grab one side of the dough, stretch it up and fold it over the center. Rotate the bowl 90 degrees and repeat until you've worked around the entire dough ball. After the second round, gently fold in the optional nuts and dried fruit if using.
Cover your dough with a damp cloth or plastic wrap and allow it to ferment at room temperature for 4-6 hours. Look for a dough that feels puffy with visible bubbles on the surface and edges. In warmer kitchens (above 75°F), check your dough at the 4-hour mark to prevent over-fermentation.
Gently transfer your dough to a lightly floured surface, being careful not to deflate it completely. Shape into a round boule or an oval batard, depending on your baking vessel. Place the shaped dough into a well-floured banneton or a parchment-lined bowl, seam side up. Cover and refrigerate for 2-3 hours for a cold proof.
Place your Dutch oven or baking stone in the oven and preheat to 450°F (230°C) for at least 30 minutes. While the oven preheats, remove your dough from the refrigerator and allow it to sit at room temperature for 20 minutes.
Turn your dough onto parchment paper. Using a very sharp knife or bread lame, score the top with a decisive 1/4-inch deep cut. Carefully transfer the dough on the parchment into your preheated Dutch oven. Bake covered for 25 minutes to trap steam, then remove the lid and reduce temperature to 425°F. Continue baking for 20-25 more minutes until the crust is deep golden brown and the internal temperature reaches 205°F (96°C).
Allow your sourdough pumpkin bread to cool completely on a wire rack for at least 2 hours before slicing. This critical cooling period allows the crumb to set properly and flavors to fully develop.