Preheat your oven to 350 deg F. And line 12 liners in muffin tray and set it aside.
In a mixing bowl beat butter and sugar together until creamed and fluffy. About 3 minutes.
Add ripen bananas and mash with a fork. Now add your room temperature egg and vanilla, Beat it all in.
Next, sift all the dry ingredients (flour, baking powder, soda and salt) over wet. Fold them in with a spatula. Also fold in the blueberries. Do not thaw if using frozen berries!
Pour in the prepared liners, top with crumb topping, sugar and bake for 23-25 minutes. Or until they pass toothpick test. Enjoy warm!