Preheat the oven to 425°F and prepare a 12-cup muffin tin with paper muffin liners.
Add flour, baking powder, sugar, and salt in a bowl and give it a whisk with a fork.
In a mixing bowl combine the eggs, vanilla, melted butter, sour cream, oil, and mashed bananas and whisk together.
Add the liquid ingredients to the dry ingredients.
Gently fold just until the dry ingredients are wet. Lumps are okay when making muffins. You do not want to mix until the batter is smooth.
Gently fold in the blueberries, just until lightly coated in batter.
Line a cupcake tin with paper liners. Scoop 1/4 cup into each cupcake liner.
In a small bowl, combine streusel ingredients and then sprinkle 1-2 tablespoons over each cupcake batter.
In a preheated 425-degree oven, bake for 12 minutes until golden brown.