Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it lightly.
In a large bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt.
In another bowl, combine the melted butter, buttermilk, eggs, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined. Gently fold in the blueberries.
In a separate bowl, prepare the crumb topping by mixing together the flour, brown sugar, softened butter, and cinnamon until crumbly.
Scoop the muffin batter into the prepared muffin tin, filling each cup about two-thirds full.
Sprinkle the crumb topping generously over each muffin.
Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.