Preheat oven to 425 degrees. Line or grease a 12 cup muffin tin.
In a medium bowl, whisk together sugar, mashed bananas, milk, oil, egg, and vanilla extract. In a separate bowl combine the flour, baking powder, and salt. Gently stir the flour mixture into the wet ingredients, do not over mix.
In a small bowl gently toss the blueberries in a little bit of flour to help them from sinking to the bottom of the muffins. Gently fold them into the batter. Scoop batter evenly into prepared muffin pan.
In a small bowl combine the crumble ingredients. Spoon evenly on top of each muffin. Bake at 425 degrees for 7 minutes, then reduce heat to 350 degrees while the muffins stay in the oven. Bake for an additional 10-15 minutes or until a toothpick comes out clean.
Cool on a cooling rack. Muffins will be dense. Best served warm with butter!
These muffins are denser than a cake-like fluffy muffin.
See blog post for the reason for the two temperature baking!