In a large bowl, whisk together sourdough starter, milk, sugar, pumpkin spice, melted butter, and flour until smooth.
Cover and let ferment at room temperature for up to 12 hours.
In the morning, add eggs, baking soda, baking powder, pumpkin puree, and salt. Stir well.
Rest the batter for 20 minutes while preheating your waffle iron.
Cook as above, 3–5 minutes per side.