Preheat the oven to 425F. Grease an entire standard-size muffin pan (including the rim) with butter or spray with non-stick cooking spray.
To prepare the streusel; mix together the sugar, flour, and cinnamon in a small bowl. Stir in the butter, and set aside.
In a large bowl, whisk the flour, baking powder, baking soda, and salt together. Set aside.
In a medium bowl, whisk the melted butter with the sugar. Add the eggs, milk, and vanilla. Mix again.
Add the wet ingredients to the dry ingredients and gently stir using a rubber spatula until almost combined. Fold in the blueberries until just combined.
Divide the batter into the 12 muffin cups, filling all the way to the top. Sprinkle with the streusel.
Bake for 5 minutes at 425F, then keeping the muffins in the oven, reduce the heat to 375F and bake for another 15 minutes or until a toothpick inserted into the center comes out clean.
Let cool in pan on the countertop for 10 minutes. Carefully remove and transfer to wire rack.
