01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, mash bananas then whisk in eggs, vegetable oil, yogurt or sour cream, and vanilla extract until smooth.
03 - In a separate bowl, whisk together flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and cinnamon if using.
04 - Gently fold dry ingredients into wet mixture until just combined; avoid overmixing.
05 - Fold chocolate chips and chopped walnuts into the batter evenly.
06 - Distribute batter evenly among muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 22 minutes, until a toothpick inserted into the center emerges clean or with a few moist crumbs.
08 - Let muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely.