Preheat oven to 375 degrees.
In a small bowl, mix together the streusel ingredients. Set aside.
In a medium bowl, mix together the flour, sugar, baking powder, and baking soda.
In a separate bowl, combine the milk, butter, egg, and vanilla.
Pour the wet ingredients into the bowl with the dry ingredients and mix until just combined. Do not over mix.
Gently stir in the blueberries.
Spoon the batter into a muffin pan that has been prepared with non-stick spray.
Sprinkle the streusel topping over the batter.
Bake at 375 degrees for 15 - 20 minutes or until the muffins are golden.