Preheat oven to 400 degrees. Line a 12 cup muffin pan with paper liners and set aside.
In a medium bowl mix flour, baking powder and salt.
In a large bowl mix milk, sugar, melted butter, eggs, lemon zest and vanilla until blended.
Gradually stir in flour mixture into wet ingredients until just combined.
Gently fold in blueberries.
Divide batter evenly among muffins cups.
To make brown sugar crumble, mix together flour and brown sugar until combined. Add 4 tablespoons of softened butter and mix until crumbly, add additional butter if needed. Sprinkle evenly on top of muffins.
Bake for 18-20 minutes until golden brown and tester inserted into the center of the muffins comes out clean.