Preheat the oven to 350°F (175°C). Grease or line a 8 × 5-inch (20 × 13 cm) loaf pan with parchment paper, leaving an overhang so you can lift out the loaf.
In a bowl, whisk together the flour, 1 1/2 teaspoons cinnamon, ginger, nutmeg, cloves, salt, baking soda, and baking powder. 190 g all-purpose flour, 1 1/2 tsp ground cinnamon, 1/4 tsp ground ginger, 1/4 tsp ground nutmeg, 1/8 tsp ground cloves, 3/4 tsp salt, 1 tsp baking soda, 1/4 tsp baking powder
In a large bowl, whisk together the 100 g granulated sugar, brown sugar, and oil. Whisk in the eggs, pumpkin puree, sourdough discard, milk, and vanilla until well combined. 100 g granulated sugar, 100 g soft brown sugar, 105 g vegetable oil, 2 large eggs, 226 g pumpkin puree, 100 g sourdough discard , 60 g whole milk, 1 tsp vanilla paste
Add the dry ingredients to the wet ingredients and fold gently until just combined. Do not overmix.
In a small bowl, combine the sugar and cinnamon for the swirl. 65 g granulated sugar, 1 Tbsp ground cinnamon
Spread one-third of the batter into the prepared pan and sprinkle with just under half the cinnamon sugar mixture.
Spread another third of batter gently over the cinnamon sugar. Sprinkle with almost all the remaining cinnamon sugar, reserving about 1 teaspoon for the top.
Spread the final third of batter over the top. Run a butter knife or skewer gently through the batter a few times to create cinnamon sugar ribbons without fully mixing the layers.
Sprinkle the reserved teaspoon of cinnamon sugar evenly over the surface.
Bake for 55 to 70 minutes until a skewer inserted into the pumpkin crumb comes out without wet batter. Cinnamon sugar might leave a bit of sticky mark so test in more than one spot. Loosely cover with foil if the top browns too quickly.
Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.
Notes
Store airtight at room temperature up to 3 days, refrigerate up to 5 days, or freeze up to 3 months.