Preheat oven to 350°
Melt butter and let cool.
Using a stand mixer with paddle attachment, mix cooled melted butter and sugars together.
Add in smashed bananas, eggs and vanilla extract and mix until incorporated.
In a separate bowl, mix together flour, baking powder, baking soda, salt, and cinnamon.
Pour dry ingredients into wet and stir with wooden spoon to incorporate. Don't over mix.
Add Blueberries (or Chocolate Chips) and stir to combine.
In a separate bowl, make the streusel topping by mixing dry ingredients together, pour in melted butter and use a fork or your hand to incorporate making sure to leave bigger clumps.
Scoop your batter into prepared muffin tin or muffin liners, and sprinkle streusel topping on top.
Bake for 23-25 minutes until toothpick comes out clean.
Let cool for 5 minutes.
Slather with butter and Enjoy!