1. 1. Prepare Your Baking Pan and Preheat the Oven: Start by preheating your oven to 350 F (175 C). Lightly grease and flour a 9×5-inch loaf pan, or line it with parchment paper, leaving an overhang on the long sides to easily lift the loaf out later. This prevents sticking and ensures a clean release.

2. 2. Combine Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking soda, salt, and pumpkin pie spice. Make sure there are no lumps and the spices are evenly distributed throughout the flour mixture. Set this aside.

3. 3. Cream Wet Ingredients: In a large mixing bowl, using an electric mixer or a sturdy whisk, cream together the softened unsalted butter, granulated sugar, and light brown sugar until the mixture is light and fluffy. This usually takes about 2-3 minutes. Scrape down the sides of the bowl as needed to ensure everything is well combined.

4. 4. Incorporate Eggs and Wet Additions: Beat in the eggs one at a time, mixing well after each addition until fully incorporated. Then, add the pumpkin puree, sourdough discard, and vanilla extract. Mix on low speed until just combined. The mixture might look a little curdled at this stage, but don’t worry, it will come together.

5. 5. Combine Wet and Dry Mixtures: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; overmixing can lead to a tough loaf. A few streaks of flour are fine, as they will disappear during baking. If using, gently fold in the chopped pecans or walnuts at this stage.

6. 6. Bake the Loaf: Pour the batter evenly into your prepared loaf pan. Place the pan in the preheated oven and bake for 50-60 minutes, or until a wooden skewer or toothpick inserted into the center of the loaf comes out clean. The top should be golden brown and spring back lightly when touched.

7. 7. Cool and Glaze (Optional): Once baked, remove the loaf from the oven and let it cool in the pan for about 10-15 minutes before carefully lifting it out onto a wire rack to cool completely. If you’re making the glaze, whisk together the powdered sugar, milk or cream, and vanilla extract in a small bowl until smooth. Drizzle the glaze over the cooled loaf just before serving.