1. Preheat oven to 350°F (175°C) and line a 12-cup muffin tin or grease it lightly.

2. In a bowl whisk together flour, baking powder, baking soda, cinnamon, and salt.

3. In a separate bowl combine sourdough starter discard, brown sugar, granulated sugar, eggs, oil, and vanilla until smooth.

4. Fold grated carrots into the wet mixture.

5. Gradually add dry ingredients to the wet mixture, stirring until just combined.

6. Fold in chopped walnuts if using, being careful not to overmix.

7. Divide batter evenly among muffin cups, filling each about two-thirds full.

8. Bake for 18–22 minutes or until a toothpick inserted into the center comes out clean.

9. Allow muffins to rest in the tin for 5 minutes, then transfer to a wire rack to cool completely.

10. Serve warm or at room temperature.