Preheat your oven to 350°F (175°C). Grease and flour a 9×5 inch loaf pan.
In a large bowl, whisk together the active sourdough starter, pumpkin puree, granulated sugar, brown sugar, melted butter, eggs, and vanilla extract until well combined.
In a separate bowl, whisk together the all-purpose flour, pumpkin pie spice, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
If using, prepare the streusel topping by combining the ingredients in a small bowl until crumbly.
Pour the batter into the prepared loaf pan. If using streusel, sprinkle it evenly over the top.
Bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out clean.
Let the bread cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
If desired, prepare the glaze by mixing powdered sugar, milk, and vanilla extract until smooth. Drizzle over the cooled bread.
Notes
For a tangier flavor, you can use sourdough discard instead of active starter, but you may need to adjust the leavening slightly.
This recipe can also be used to make pumpkin sourdough muffins. Bake for 20-25 minutes at 350°F (175°C).
Ensure your pumpkin puree is not pumpkin pie filling, which contains added sugar and spices.