Preheat the oven to 325 degrees F. Grease a 9" x 5" loaf pan with butter and set aside.
In a large mixing bowl, whisk together the flour, pumpkin pie spice, baking powder, baking soda and salt until combined.
In a separate large bowl (or the bowl of a stand mixer), cream together softened butter and sugars. Add the egg and beat well. Then add vanilla, pumpkin puree, and sourdough starter. Mix until combined.
Add the dry ingredients to the wet ingredients and mix until just combined.
Pour batter into the prepared loaf pan. The batter will be very thick.
Bake for 60-75 minutes or until a toothpick or wooden skewer inserted into the center of the loaf comes out clean.
If the top of the bread is already brown, but the inside hasn't finished cooking, tent a piece of aluminum foil over the top of the bread to keep the top from burning.
Cool in pan 10-15 minutes, then remove from pan to finish cooling on a wire rack.
Notes
This is a sourdough discard pumpkin bread recipe, so it uses sourdough discard rather than an active starter.
Instead of canned pumpkin purée you can make your own pumpkin puree with a fresh pumpkin following these instructions.
Instead of the pumpkin pie spice called for in the recipe, you can use: 1 tsp ground cinnamon, 1 tsp ground cloves, and 1 tsp ground nutmeg.
This bread can be made ahead and frozen for up to three months.
This recipe uses a 9" x 5" loaf pan. However, the cook time is much longer with a loaf this size. You could also divide the batter between two smaller loaf pans, such as 8" x 4" size pans.