1. Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with paper liners or grease it lightly.

2. Mash the ripe bananas in a large bowl until mostly smooth with a few small chunks remaining.

3. Whisk in the eggs, honey or brown sugar, melted butter or coconut oil, milk, and sourdough starter until combined.

4. In a separate bowl, whisk together the whole wheat flour, protein powder, baking powder, baking soda, cinnamon, and salt.

5. Gently fold the dry ingredients into the wet mixture until just combined and no flour streaks remain.

6. Fold in optional chocolate chips or chopped nuts if using.

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

8. Bake for 18–22 minutes until the tops are golden and a toothpick inserted comes out clean.

9. Let the muffins rest in the pan for 5–10 minutes to firm up.

10. Transfer the muffins to a cooling rack to cool completely before storing.

11. Store cooled muffins in an airtight container at room temperature for up to 3 days, refrigerate up to 5 days, or freeze up to 2 months.