Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it lightly.
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, combine the melted butter, egg, buttermilk, and vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Gently fold in the blueberries, being careful not to overmix.
In a separate bowl, prepare the crumb topping by mixing the flour, granulated sugar, brown sugar, softened butter, and cinnamon until crumbly.
Fill each muffin cup about 2/3 full with the batter and sprinkle the crumb topping generously over each muffin.
Bake for 18-20 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.