• Before you begin, you will get the best results if you mash the bananas first then measure out the exact amount needed.
• Preheat the oven to 425°F (you will reduce the temperature after the muffins cook for 5 minutes)
• Grease 12 standard-sized muffin tins or line them with paper baking cups. In a medium bowl, whisk all the dry ingredients together then set aside.
• In another bowl, beat the butter and brown sugar then add the eggs and beat until well blended. Next add the vanilla, and mashed bananas and beat until well combined.
• Fold the wet mixture into the flour mixture then fold in the blueberries.

Make the cinnamon crumb topping:

• Blend the flour, sugar, and cinnamon together then stir in the melted butter until you have pea-sized clumps.
• Fill the greased muffin tins completely full with the batter then sprinkle the tops with the cinnamon crumb topping. For slightly smaller muffins, you can fill the tins ¾ full which will give you 18 muffins (but you will need to reduce the baking time by a couple minutes).
• Bake in the preheated oven at 425°F for 5 minutes then turn the oven down to 350°F and bake for 12 to16 more minutes or until a toothpick inserted in the center comes out clean.
• Allow the muffins to cool for at least 10 minutes before removing from the muffin tins. The tender muffins can fall apart if you remove them while they are still warm.