Preheat the oven to 375°F (190°C) and line a muffin tin with paper liners.

In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.

In another bowl, combine the buttermilk, melted butter, eggs, and vanilla extract.

Pour the wet ingredients into the dry ingredients and mix until just combined. Gently fold in the blueberries.

In a small bowl, mix together the flour, brown sugar, and cinnamon. Cut in the cold butter until the mixture resembles coarse crumbs.

Spoon the muffin batter into the prepared muffin tin, filling each cup about 2/3 full.

Sprinkle the streusel topping evenly over each muffin.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

Let the muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.