1. 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.

2. In a large mixing bowl, whisk together the all-purpose flour, whole wheat flour, granulated sugar, brown sugar, cinnamon, nutmeg, ginger, baking soda, and salt. Make sure there are no lumps and the spices are evenly distributed.

3. In a separate medium bowl, whisk together the sourdough discard, milk, vegetable oil, egg, and vanilla extract until well combined and smooth.

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

5. Gently fold in the grated apple, grated carrots, and optional walnuts/pecans and raisins/dried cranberries. Distribute them evenly throughout the batter.

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

7. Place the muffin tin in the preheated oven and 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 when lightly touched.

8. Once baked, remove the muffin tin from the oven and let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. Enjoy them warm or at room temperature.