In a large bowl, whisk together 1 cup of active sourdough starter, 1 cup of pumpkin puree, and 1/2 cup of lukewarm water until smooth. Gradually add 3 cups of bread flour, 1 teaspoon of salt, and any optional spices like cinnamon or nutmeg. Mix until a shaggy dough forms, ensuring that all the flour is incorporated.

Cover the bowl with a kitchen towel or plastic wrap and let the dough rest for 30 to 45 minutes at room temperature.

Perform 3 to 4 sets of stretch-and-fold on the dough every 30 minutes over a period of 2 to 3 hours.

Shape the dough into a round loaf and place it seam-side up in a floured proofing basket.

Allow the shaped dough to proof at room temperature for 2 to 4 hours, or refrigerate overnight.

Preheat your oven to 450°F (230°C), placing a Dutch oven inside to heat for 30 minutes. Invert the dough onto parchment paper, score the top, and bake covered for the first 20 minutes.

Remove the lid and bake uncovered for an additional 20 to 25 minutes until the crust is a deep golden brown.

Carefully transfer the bread to a wire rack and allow to cool for at least 1 hour before slicing.