Preheat oven to 400°.
Combine flour, baking soda, baking powder, cinnamon & salt. Sift or whisk ingredients together to combine & set aside.
In a separate bowl, combine brown sugar, white sugar, mashed bananas, eggs, butter, sour cream & vanilla extract. Combine this very well, ensure no egg whites are visible in the batter.
Add flour mixture to banana mixture with a spatula, combine gently but well. Do not leave streaks of flour but stop mixing the second there is no flour visible. Fold in chocolate chips.
Grease muffin tin holes & top of pan with butter. Make sure you grease it well.
Fill muffin tins to top of the tin. Do not fill ¾, fill to the top. Sprinkle tops with sugar.
Let batter rest in pan for 15 minutes before baking, this is optional but recommended for a better rise.
Bake for 5 minutes, then lower the temp to 375° & bake another 11-15 minutes, or until a toothpick inserted in the centre has crumbs on it but no liquidy batter. If it comes out completely clean, this may mean your muffins are overcooked.
Let cool in tray for 5 minutes then remove to a wire rack or a plate/serving tray.
