Preheat oven to 400 degrees.
Oil your bread loaf pan and set aside.
Melt a stick of butter on the stove. Make sure it's just melted before adding it to the bowl.
Wait for the butter to cool before adding other ingredients. Tip - to speed up the procees I fill a bowl with ice water and put the bottom of the bowl in the water until it's room temp.
Once the butter is at room temperature, add a cup of pumpkin puree, a cup of brown sugar, 1/2 a cup of starter, 1 teaspoon of vanilla, and 1 egg to your stand mixer or bowl and whisk together.
Once the wet ingredients are well-incorporated, add 1 1/2 cup of flour, 1/2 teaspoon of salt, 1 teaspoon of baking powder and baking soda, 1 tablespoon of pumpkin spice, and 1 teaspoon of cinnamon to the bowl and mix together.
Add the pumpkin cinnamon sourdough bread batter to the oiled bread pan and bake at 400 degrees for 40 minutes.
To check that the bread has baked all the way through, take a toothpick or a knife and stick it in the middle of the loaf. If it comes out clean then it is done baking.