Preheat oven to 400 degrees F. Grease bottoms of a muffin tin or line with paper cups. Prepare streusel topping by adding all streusel ingredients into a small bowl and cut into the ingredients using a pastry blender or two forks criss crossed, until you get a crumbly mixture. Set streusel topping aside. Make muffin batter by first beating milk, oil, vanilla and egg into a bowl. Once mixed, add the flour, sugar, baking powder and salt and mix thoroughly. Gently stir in the blueberries. Pour batter into 12 muffin cups and sprinkle each with the streusel topping. Bake for 20-25 minutes or until golden brown. Remove from pan onto a wire rack to cool slightly, then serve warm.