Preheat your oven to 350°F (175°C) to ensure even baking.
Line a muffin tin with paper liners or grease it with butter or non-stick spray.
In a large bowl, whisk together the white whole wheat flour, baking powder, baking soda, salt, and cinnamon (if using).
In another bowl, mix the mashed bananas, melted butter, maple syrup, eggs, yogurt, sourdough starter, and vanilla extract until well combined.
Gently fold the wet ingredients into the dry ingredients using a spatula. Don't overmix; it's okay to have a few lumps.
Fold in about 3/4 cup of the mini chocolate chips, reserving the rest for topping.
Scoop the batter into the prepared muffin tin, filling each cup about 2/3 full. Sprinkle the remaining chocolate chips on top.
Bake for 18-22 minutes, or until a toothpick inserted comes out clean.
Let the muffins cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.