Banana Blueberry Muffins with Crumb Topping
| 2 1/4 cups all-purpose flour |
| 1 Tbsp baking powder |
| 1 tsp baking soda |
| 1/2 tsp ground cinnamon |
| 1/2 tsp salt |
| 1/2 cup butter, melted |
| 3/4 cup brown sugar, packed |
| 2 large eggs |
| 2 tsp vanilla extract |
| 3 to 4 very ripe bananas, mashed |
| 2 cups fresh or frozen blueberries |
| Cinnamon Crumb Topping |
| 3/4 cup flour |
| 1/2 cup granulated sugar |
| 1 tsp ground cinnamon |
| 4 tablespoons butter, melted |