Preheat oven temperature to 375 ℉
Mix together flour, sugar, salt, and baking powder.
Add melted butter, eggs, and vanilla extract. Mix until batter is smooth.
In a separate bowl mix together salt, flour, sugar, and brown sugar.
Add melted butter and mix until the streusel is crumbly.
Gently fold blueberries into muffin batter.
Fill muffin cups to the top and generously sprinkle with streusel. Press the streusel slightly into the batter.
Bake the muffins for 25 minutes or until golden brown.