Preheat the oven to 350 degrees.
Line a loaf pan with parchment paper. Make sure the parchment paper overhands the sides of the loaf pan. Set the aside.
In a small bowl, mix together the flour, baking powder, pumpkin spice, and salt.
In a large bowl, add the brown sugar, sugar, and melted butter. Mix well until all the ingredients are combined.
Add the sourdough starter, eggs, and vanilla. Mix again.
Add the pumpkin puree and mix until all the ingredients are combined.
Pour the dry ingredients into the wet ingredients. Mix until just combined. Do not overmix at this point, it's ok if there are lumps left in the batter.
Pour the batter into the prepared loaf pan. Bake for 50-60 minutes or until a toothpick is inserted and comes out clean. Let the bread cool on a wire rack before serving.