1. Prepare your oven and muffin tin: Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it well with non-stick spray. This prevents sticking and makes cleanup a breeze.

2. Combine dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, light brown sugar, pumpkin pie spice, baking soda, and salt. Make sure there are no lumps, especially in the brown sugar, so everything mixes evenly.

3. Mix wet ingredients: In a separate medium bowl, whisk together the sourdough discard, pumpkin puree, vegetable oil (or melted butter), large egg, and vanilla extract until well combined and smooth.

4. Combine wet and dry mixtures: Pour the wet ingredient mixture into the dry ingredient mixture. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will lead to a more tender muffin. Overmixing can result in tough muffins.

5. Fill muffin cups: Divide the batter evenly among the 12 prepared muffin cups. You can use an ice cream scoop for easy and consistent portioning. Fill each cup about two-thirds full.

6. Bake the muffins: Place the muffin tin in the preheated oven. Bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back lightly when touched.

7. Cool and serve: Once baked, remove the muffin tin from the oven and let the muffins cool in the tin for 5 minutes. Then, transfer them to a wire rack to cool completely. This prevents the bottoms from getting soggy.