Prep the pan and oven: Preheat oven to 350°F (177°C). Line a 9x5-inch loaf pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.

Whisk the wet ingredients: In a large bowl, whisk pumpkin, granulated sugar, brown sugar, eggs, oil, sourdough starter, and vanilla until smooth and glossy.

Combine dry ingredients: In a separate bowl, whisk flour, baking soda, baking powder, salt, cinnamon, ginger, nutmeg, and cloves.

Bring it together: Add half the dry mix to the wet and stir gently. Pour in the milk, then add the remaining dry mix. Stir just until no dry streaks remain. Do not overmix.

Pan and top: Scrape batter into the prepared pan and smooth the top. Sprinkle evenly with pepitas and, if using, turbinado sugar.

Bake: Bake 55–70 minutes, or until the top is domed and a toothpick comes out with a few moist crumbs. If the top browns too fast, tent loosely with foil for the last 15 minutes.

Cool properly: Let the loaf cool in the pan for 15 minutes. Lift out using the parchment and cool completely on a rack before slicing.