Step 1: **Mix the Autolyse (The Night Before, 8-12 hours before baking):** In a large bowl, combine the warm water and pumpkin puree. Add the bread flour and mix until just combined and no dry spots remain. Cover the bowl with a damp cloth or plastic wrap and let it rest at room temperature for 30 minutes to 1 hour (autolyse). This step hydrates the flour and begins gluten development.
Step 2: **Incorporate Starter & Salt:** Add the active sourdough starter and salt to the autolysed dough. Mix thoroughly, either by hand (squeeze and fold method) or with a stand mixer on low speed, until the starter and salt are fully incorporated. The dough will be shaggy.
Step 3: **First Bulk Fermentation & Stretch & Folds (4-6 hours):** Cover the bowl and let the dough rest for 30 minutes. Then, perform your first set of stretch and folds. Grab a portion of the dough, stretch it upwards, and fold it over itself. Rotate the bowl 90 degrees and repeat 3-4 times. Cover and rest for 30 minutes. Repeat this stretch and fold process 3-4 more times over the next 2-3 hours. After the last fold, let the dough rest undisturbed for the remainder of the 4-6 hour bulk fermentation, or until it has increased in volume by about 30-50% and feels airy and bubbly.
Step 4: **Pre-Shape:** Gently turn the dough out onto a lightly floured surface. Using a bench scraper, gently shape the dough into a loose round or rectangle. Let it rest, uncovered, for 20-30 minutes.
Step 5: **Final Shape:** Lightly flour your hands and the dough. Gently shape the dough into a tight boule (round) or batard (oval), creating tension on the surface. For a detailed visual, many online videos demonstrate proper sourdough shaping techniques.
Step 6: **Cold Proof (10-18 hours):** Place the shaped dough seam-side up into a lightly floured banneton basket or a bowl lined with a floured tea towel. Cover with plastic wrap and refrigerate for 10-18 hours. This slow cold proof develops flavor and makes the dough easier to handle.
Step 7: **Preheat Oven & Dutch Oven:** About 1 hour before baking, place your Dutch oven with its lid into your oven and preheat to 475°F (245°C).
Step 8: **Score and Bake:** Carefully remove the hot Dutch oven from the oven. Gently invert your cold dough into the hot Dutch oven. Use a sharp razor blade or lame to score the top of the dough with your desired pattern (e.g., a cross, a leaf, or a simple slash). This allows the bread to expand during baking.
Step 9: **Bake Covered:** Place the lid back on the Dutch oven and bake for 30 minutes.
Step 10: **Bake Uncovered:** Remove the lid and reduce the oven temperature to 450°F (230°C). Continue baking for another 15-20 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210°F (93-99°C).
Step 11: **Cool Completely:** Carefully remove the bread from the Dutch oven and transfer it to a wire rack. Let it cool completely for at least 2-3 hours before slicing. Slicing too early can result in a gummy texture.