Preheat your oven to 350°F (175°C). Grease a baking pan.
In a mixing bowl, combine flour, sugar, baking powder, and salt.
Add milk, vanilla extract, and blueberries. Mix until just combined.
Pour the batter into the prepared baking pan.
In a separate bowl, mix brown sugar, flour, and melted butter to make the crumb topping.
Sprinkle the crumb topping over the batter.
Bake for 45 minutes or until a toothpick comes out clean.
Let it cool before serving.